WALK_SCALAR - when SCALAR_VALUE is found
WALK_PTR - when pointer value is found, its ID is stored
in 'next_btf_id' output param
WALK_STRUCT - when nested struct object is found, its ID is stored
in 'next_btf_id' output param
It will be used in following patches to get all nested
struct objects for given type and offset.
The btf_struct_access now calls btf_struct_walk function,
as long as it gets nested structs as return value.
Jiri Olsa [Tue, 25 Aug 2020 19:21:13 +0000 (21:21 +0200)]
bpf: Move btf_resolve_size into __btf_resolve_size
Moving btf_resolve_size into __btf_resolve_size and
keeping btf_resolve_size public with just first 3
arguments, because the rest of the arguments are not
used by outside callers.
Following changes are adding more arguments, which
are not useful to outside callers. They will be added
to the __btf_resolve_size function.
The CC_CAN_LINK checks that the host compiler can link, but bpf_preload
relies on libbpf which in turn needs libelf to be present during linking.
allmodconfig runs in odd setups with cross compilers and missing host
libraries like libelf. Instead of extending kconfig with every possible
library that bpf_preload might need disallow building BPF_PRELOAD in
such build-only configurations.
KP Singh [Tue, 25 Aug 2020 18:29:19 +0000 (20:29 +0200)]
bpf: Add selftests for local_storage
inode_local_storage:
* Hook to the file_open and inode_unlink LSM hooks.
* Create and unlink a temporary file.
* Store some information in the inode's bpf_local_storage during
file_open.
* Verify that this information exists when the file is unlinked.
sk_local_storage:
* Hook to the socket_post_create and socket_bind LSM hooks.
* Open and bind a socket and set the sk_storage in the
socket_post_create hook using the start_server helper.
* Verify if the information is set in the socket_bind hook.
KP Singh [Tue, 25 Aug 2020 18:29:18 +0000 (20:29 +0200)]
bpf: Allow local storage to be used from LSM programs
Adds support for both bpf_{sk, inode}_storage_{get, delete} to be used
in LSM programs. These helpers are not used for tracing programs
(currently) as their usage is tied to the life-cycle of the object and
should only be used where the owning object won't be freed (when the
owning object is passed as an argument to the LSM hook). Thus, they
are safer to use in LSM hooks than tracing. Usage of local storage in
tracing programs will probably follow a per function based whitelist
approach.
Since the UAPI helper signature for bpf_sk_storage expect a bpf_sock,
it, leads to a compilation warning for LSM programs, it's also updated
to accept a void * pointer instead.
KP Singh [Tue, 25 Aug 2020 18:29:17 +0000 (20:29 +0200)]
bpf: Implement bpf_local_storage for inodes
Similar to bpf_local_storage for sockets, add local storage for inodes.
The life-cycle of storage is managed with the life-cycle of the inode.
i.e. the storage is destroyed along with the owning inode.
The BPF LSM allocates an __rcu pointer to the bpf_local_storage in the
security blob which are now stackable and can co-exist with other LSMs.
KP Singh [Tue, 25 Aug 2020 18:29:15 +0000 (20:29 +0200)]
bpf: Generalize bpf_sk_storage
Refactor the functionality in bpf_sk_storage.c so that concept of
storage linked to kernel objects can be extended to other objects like
inode, task_struct etc.
Each new local storage will still be a separate map and provide its own
set of helpers. This allows for future object specific extensions and
still share a lot of the underlying implementation.
adding new map operations to support bpf_local_storage maps:
* storages for different kernel objects to optionally have different
memory charging strategy (map_local_storage_charge,
map_local_storage_uncharge)
* Functionality to extract the storage pointer from a pointer to the
owning object (map_owner_storage_ptr)
KP Singh [Tue, 25 Aug 2020 18:29:14 +0000 (20:29 +0200)]
bpf: Generalize caching for sk_storage.
Provide the a ability to define local storage caches on a per-object
type basis. The caches and caching indices for different objects should
not be inter-mixed as suggested in:
Yonghong Song [Mon, 24 Aug 2020 22:28:07 +0000 (15:28 -0700)]
selftests/bpf: Enable tc verbose mode for test_sk_assign
Currently test_sk_assign failed verifier with llvm11/llvm12.
During debugging, I found the default verifier output is
truncated like below
Verifier analysis:
Skipped 2200 bytes, use 'verb' option for the full verbose log.
[...]
off=23,r=34,imm=0) R5=inv0 R6=ctx(id=0,off=0,imm=0) R7=pkt(id=0,off=0,r=34,imm=0) R10=fp0
80: (0f) r7 += r2
last_idx 80 first_idx 21
regs=4 stack=0 before 78: (16) if w3 == 0x11 goto pc+1
when I am using "./test_progs -vv -t assign".
The reason is tc verbose mode is not enabled.
This patched enabled tc verbose mode and the output looks like below
Verifier analysis:
Daniel T. Lee [Sun, 23 Aug 2020 08:53:34 +0000 (17:53 +0900)]
samples: bpf: Refactor tracepoint tracing programs with libbpf
For the problem of increasing fragmentation of the bpf loader programs,
instead of using bpf_loader.o, which is used in samples/bpf, this
commit refactors the existing tracepoint tracing programs with libbbpf
bpf loader.
- Adding a tracepoint event and attaching a bpf program to it was done
through bpf_program_attach().
- Instead of using the existing BPF MAP definition, MAP definition
has been refactored with the new BTF-defined MAP format.
Daniel T. Lee [Sun, 23 Aug 2020 08:53:33 +0000 (17:53 +0900)]
samples: bpf: Refactor kprobe tracing programs with libbpf
For the problem of increasing fragmentation of the bpf loader programs,
instead of using bpf_loader.o, which is used in samples/bpf, this
commit refactors the existing kprobe tracing programs with libbbpf
bpf loader.
- For kprobe events pointing to system calls, the SYSCALL() macro in
trace_common.h was used.
- Adding a kprobe event and attaching a bpf program to it was done
through bpf_program_attach().
- Instead of using the existing BPF MAP definition, MAP definition
has been refactored with the new BTF-defined MAP format.
Daniel T. Lee [Sun, 23 Aug 2020 08:53:32 +0000 (17:53 +0900)]
samples: bpf: Cleanup bpf_load.o from Makefile
Since commit cc7f641d637b ("samples: bpf: Refactor BPF map performance
test with libbpf") has ommited the removal of bpf_load.o from Makefile,
this commit removes the bpf_load.o rule for targets where bpf_load.o is
not used.
Andrii Nakryiko [Fri, 21 Aug 2020 22:56:53 +0000 (15:56 -0700)]
libbpf: Fix type compatibility check copy-paste error
Fix copy-paste error in types compatibility check. Local type is accidentally
used instead of target type for the very first type check strictness check.
This can result in potentially less strict candidate comparison. Fix the
error.
Jakub Sitnicki [Fri, 21 Aug 2020 10:02:26 +0000 (12:02 +0200)]
bpf: sk_lookup: Add user documentation
Describe the purpose of BPF sk_lookup program, how it can be attached, when
it gets invoked, and what information gets passed to it. Point the reader
to examples and further documentation.
====================
The earlier effort in BPF-TCP-CC allows the TCP Congestion Control
algorithm to be written in BPF. It opens up opportunities to allow
a faster turnaround time in testing/releasing new congestion control
ideas to production environment.
The same flexibility can be extended to writing TCP header option.
It is not uncommon that people want to test new TCP header option
to improve the TCP performance. Another use case is for data-center
that has a more controlled environment and has more flexibility in
putting header options for internal traffic only.
This patch set introduces the necessary BPF logic and API to
allow bpf program to write and parse header options.
There are also some changes to TCP and they are mostly to provide
the needed sk and skb info to the bpf program to make decision.
Patch 9 is the main patch and has more details on the API and design.
The set includes an example which sends the max delay ack in
the BPF TCP header option and the receiving side can
then adjust its RTO accordingly.
v5:
- Move some of the comments from git commit message to the UAPI bpf.h
in patch 9
- Some variable clean up in the tests (patch 11).
v4:
- Since bpf-next is currently closed, tag the set with RFC to keep the
review cadence
- Separate tcp changes in its own patches (5, 6, 7). It is a bit
tricky since most of the tcp changes is to call out the bpf prog to
write and parse the header. The write and parse callout has been
modularized into a few bpf_skops_* function in v3.
This revision (v4) tries to move those bpf_skops_* functions into separate
TCP patches. However, they will be half implemented to highlight
the changes to the TCP stack, mainly:
- when the bpf prog will be called in the TCP stack and
- what information needs to pump through the TCP stack to the actual bpf
prog callsite.
The bpf_skops_* functions will be fully implemented in patch 9 together
with other bpf pieces.
- Use struct_size() in patch 1 (Eric)
- Add saw_unknown to struct tcp_options_received in patch 4 (Eric)
v3:
- Add kdoc for tcp_make_synack (Jakub Kicinski)
- Add BPF_WRITE_HDR_TCP_CURRENT_MSS and BPF_WRITE_HDR_TCP_SYNACK_COOKIE
in bpf.h to give a clearer meaning to sock_ops->args[0] when
writing header option.
- Rename BPF_SOCK_OPS_PARSE_UNKWN_HDR_OPT_CB_FLAG
to BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG
v2:
- Instead of limiting the bpf prog to write experimental
option (kind:254, magic:0xeB9F), this revision allows the bpf prog to
write any TCP header option through the bpf_store_hdr_opt() helper.
That will allow different bpf-progs to write its own
option and the helper will guarantee there is no duplication.
- Add bpf_load_hdr_opt() helper to search a particular option by kind.
Some of the get_syn logic is refactored to bpf_sock_ops_get_syn().
- Since bpf prog is no longer limited to option (254, 0xeB9F),
the TCP_SKB_CB(skb)->bpf_hdr_opt_off is no longer needed.
Instead, when there is any option kernel cannot recognize,
the bpf prog will be called if the
BPF_SOCK_OPS_PARSE_UNKWN_HDR_OPT_CB_FLAG is set.
[ The "unknown_opt" is learned in tcp_parse_options() in patch 4. ]
- Add BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG.
If this flag is set, the bpf-prog will be called
on all tcp packet received at an established sk.
It will be useful to ensure a previously written header option is
received by the peer.
e.g. The latter test is using this on the active-side during syncookie.
- The test_tcp_hdr_options.c is adjusted accordingly
to test writing both experimental and regular TCP header option.
- The test_misc_tcp_hdr_options.c is added to mainly
test different cases on the new helpers.
- Break up the TCP_BPF_RTO_MIN and TCP_BPF_DELACK_MAX into
two patches.
- Directly store the tcp_hdrlen in "struct saved_syn" instead of
going back to the tcp header to obtain it by "th->doff * 4"
- Add a new optval(==2) for setsockopt(TCP_SAVE_SYN) such
that it will also store the mac header (patch 9).
====================
Martin KaFai Lau [Thu, 20 Aug 2020 19:01:23 +0000 (12:01 -0700)]
tcp: bpf: Optionally store mac header in TCP_SAVE_SYN
This patch is adapted from Eric's patch in an earlier discussion [1].
The TCP_SAVE_SYN currently only stores the network header and
tcp header. This patch allows it to optionally store
the mac header also if the setsockopt's optval is 2.
It requires one more bit for the "save_syn" bit field in tcp_sock.
This patch achieves this by moving the syn_smc bit next to the is_mptcp.
The syn_smc is currently used with the TCP experimental option. Since
syn_smc is only used when CONFIG_SMC is enabled, this patch also puts
the "IS_ENABLED(CONFIG_SMC)" around it like the is_mptcp did
with "IS_ENABLED(CONFIG_MPTCP)".
The mac_hdrlen is also stored in the "struct saved_syn"
to allow a quick offset from the bpf prog if it chooses to start
getting from the network header or the tcp header.
Suggested-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/bpf/20200820190123.2886935-1-kafai@fb.com
Martin KaFai Lau [Thu, 20 Aug 2020 19:01:17 +0000 (12:01 -0700)]
bpf: selftests: Tcp header options
This patch adds tests for the new bpf tcp header option feature.
test_tcp_hdr_options.c:
- It tests header option writing and parsing in 3WHS: regular
connection establishment, fastopen, and syncookie.
- In syncookie, the passive side's bpf prog is asking the active side
to resend its bpf header option by specifying a RESEND bit in the
outgoing SYNACK. handle_active_estab() and write_nodata_opt() has
some details.
- handle_passive_estab() has comments on fastopen.
- It also has test for header writing and parsing in FIN packet.
- Most of the tests is writing an experimental option 254 with magic 0xeB9F.
- The no_exprm_estab() also tests writing a regular TCP option
without any magic.
test_misc_tcp_options.c:
- It is an one directional test. Active side writes option and
passive side parses option. The focus is to exercise
the new helpers and API.
- Testing the new helper: bpf_load_hdr_opt() and bpf_store_hdr_opt().
- Testing the bpf_getsockopt(TCP_BPF_SYN).
- Negative tests for the above helpers.
- Testing the sock_ops->skb_data.
Martin KaFai Lau [Thu, 20 Aug 2020 19:01:04 +0000 (12:01 -0700)]
bpf: tcp: Allow bpf prog to write and parse TCP header option
[ Note: The TCP changes here is mainly to implement the bpf
pieces into the bpf_skops_*() functions introduced
in the earlier patches. ]
The earlier effort in BPF-TCP-CC allows the TCP Congestion Control
algorithm to be written in BPF. It opens up opportunities to allow
a faster turnaround time in testing/releasing new congestion control
ideas to production environment.
The same flexibility can be extended to writing TCP header option.
It is not uncommon that people want to test new TCP header option
to improve the TCP performance. Another use case is for data-center
that has a more controlled environment and has more flexibility in
putting header options for internal only use.
For example, we want to test the idea in putting maximum delay
ACK in TCP header option which is similar to a draft RFC proposal [1].
This patch introduces the necessary BPF API and use them in the
TCP stack to allow BPF_PROG_TYPE_SOCK_OPS program to parse
and write TCP header options. It currently supports most of
the TCP packet except RST.
Supported TCP header option:
───────────────────────────
This patch allows the bpf-prog to write any option kind.
Different bpf-progs can write its own option by calling the new helper
bpf_store_hdr_opt(). The helper will ensure there is no duplicated
option in the header.
By allowing bpf-prog to write any option kind, this gives a lot of
flexibility to the bpf-prog. Different bpf-prog can write its
own option kind. It could also allow the bpf-prog to support a
recently standardized option on an older kernel.
Sockops Callback Flags:
──────────────────────
The bpf program will only be called to parse/write tcp header option
if the following newly added callback flags are enabled
in tp->bpf_sock_ops_cb_flags:
BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG
BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG
BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG
A few words on the PARSE CB flags. When the above PARSE CB flags are
turned on, the bpf-prog will be called on packets received
at a sk that has at least reached the ESTABLISHED state.
The parsing of the SYN-SYNACK-ACK will be discussed in the
"3 Way HandShake" section.
The default is off for all of the above new CB flags, i.e. the bpf prog
will not be called to parse or write bpf hdr option. There are
details comment on these new cb flags in the UAPI bpf.h.
sock_ops->skb_data and bpf_load_hdr_opt()
─────────────────────────────────────────
sock_ops->skb_data and sock_ops->skb_data_end covers the whole
TCP header and its options. They are read only.
The new bpf_load_hdr_opt() helps to read a particular option "kind"
from the skb_data.
Please refer to the comment in UAPI bpf.h. It has details
on what skb_data contains under different sock_ops->op.
3 Way HandShake
───────────────
The bpf-prog can learn if it is sending SYN or SYNACK by reading the
sock_ops->skb_tcp_flags.
* Passive side
When writing SYNACK (i.e. sock_ops->op == BPF_SOCK_OPS_WRITE_HDR_OPT_CB),
the received SYN skb will be available to the bpf prog. The bpf prog can
use the SYN skb (which may carry the header option sent from the remote bpf
prog) to decide what bpf header option should be written to the outgoing
SYNACK skb. The SYN packet can be obtained by getsockopt(TCP_BPF_SYN*).
More on this later. Also, the bpf prog can learn if it is in syncookie
mode (by checking sock_ops->args[0] == BPF_WRITE_HDR_TCP_SYNACK_COOKIE).
The bpf prog can store the received SYN pkt by using the existing
bpf_setsockopt(TCP_SAVE_SYN). The example in a later patch does it.
[ Note that the fullsock here is a listen sk, bpf_sk_storage
is not very useful here since the listen sk will be shared
by many concurrent connection requests.
Extending bpf_sk_storage support to request_sock will add weight
to the minisock and it is not necessary better than storing the
whole ~100 bytes SYN pkt. ]
When the connection is established, the bpf prog will be called
in the existing PASSIVE_ESTABLISHED_CB callback. At that time,
the bpf prog can get the header option from the saved syn and
then apply the needed operation to the newly established socket.
The later patch will use the max delay ack specified in the SYN
header and set the RTO of this newly established connection
as an example.
The received ACK (that concludes the 3WHS) will also be available to
the bpf prog during PASSIVE_ESTABLISHED_CB through the sock_ops->skb_data.
It could be useful in syncookie scenario. More on this later.
There is an existing getsockopt "TCP_SAVED_SYN" to return the whole
saved syn pkt which includes the IP[46] header and the TCP header.
A few "TCP_BPF_SYN*" getsockopt has been added to allow specifying where to
start getting from, e.g. starting from TCP header, or from IP[46] header.
The new getsockopt(TCP_BPF_SYN*) will also know where it can get
the SYN's packet from:
- (a) the just received syn (available when the bpf prog is writing SYNACK)
and it is the only way to get SYN during syncookie mode.
or
- (b) the saved syn (available in PASSIVE_ESTABLISHED_CB and also other
existing CB).
The bpf prog does not need to know where the SYN pkt is coming from.
The getsockopt(TCP_BPF_SYN*) will hide this details.
Similarly, a flags "BPF_LOAD_HDR_OPT_TCP_SYN" is also added to
bpf_load_hdr_opt() to read a particular header option from the SYN packet.
* Fastopen
Fastopen should work the same as the regular non fastopen case.
This is a test in a later patch.
* Syncookie
For syncookie, the later example patch asks the active
side's bpf prog to resend the header options in ACK. The server
can use bpf_load_hdr_opt() to look at the options in this
received ACK during PASSIVE_ESTABLISHED_CB.
* Active side
The bpf prog will get a chance to write the bpf header option
in the SYN packet during WRITE_HDR_OPT_CB. The received SYNACK
pkt will also be available to the bpf prog during the existing
ACTIVE_ESTABLISHED_CB callback through the sock_ops->skb_data
and bpf_load_hdr_opt().
* Turn off header CB flags after 3WHS
If the bpf prog does not need to write/parse header options
beyond the 3WHS, the bpf prog can clear the bpf_sock_ops_cb_flags
to avoid being called for header options.
Or the bpf-prog can select to leave the UNKNOWN_HDR_OPT_CB_FLAG on
so that the kernel will only call it when there is option that
the kernel cannot handle.
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:58 +0000 (12:00 -0700)]
bpf: sock_ops: Change some members of sock_ops_kern from u32 to u8
A later patch needs to add a few pointers and a few u8 to
sock_ops_kern. Hence, this patch saves some spaces by moving
some of the existing members from u32 to u8 so that the later
patch can still fit everything in a cacheline.
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:52 +0000 (12:00 -0700)]
bpf: tcp: Add bpf_skops_hdr_opt_len() and bpf_skops_write_hdr_opt()
The bpf prog needs to parse the SYN header to learn what options have
been sent by the peer's bpf-prog before writing its options into SYNACK.
This patch adds a "syn_skb" arg to tcp_make_synack() and send_synack().
This syn_skb will eventually be made available (as read-only) to the
bpf prog. This will be the only SYN packet available to the bpf
prog during syncookie. For other regular cases, the bpf prog can
also use the saved_syn.
When writing options, the bpf prog will first be called to tell the
kernel its required number of bytes. It is done by the new
bpf_skops_hdr_opt_len(). The bpf prog will only be called when the new
BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG is set in tp->bpf_sock_ops_cb_flags.
When the bpf prog returns, the kernel will know how many bytes are needed
and then update the "*remaining" arg accordingly. 4 byte alignment will
be included in the "*remaining" before this function returns. The 4 byte
aligned number of bytes will also be stored into the opts->bpf_opt_len.
"bpf_opt_len" is a newly added member to the struct tcp_out_options.
Then the new bpf_skops_write_hdr_opt() will call the bpf prog to write the
header options. The bpf prog is only called if it has reserved spaces
before (opts->bpf_opt_len > 0).
The bpf prog is the last one getting a chance to reserve header space
and writing the header option.
These two functions are half implemented to highlight the changes in
TCP stack. The actual codes preparing the bpf running context and
invoking the bpf prog will be added in the later patch with other
necessary bpf pieces.
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:46 +0000 (12:00 -0700)]
bpf: tcp: Add bpf_skops_parse_hdr()
The patch adds a function bpf_skops_parse_hdr().
It will call the bpf prog to parse the TCP header received at
a tcp_sock that has at least reached the ESTABLISHED state.
For the packets received during the 3WHS (SYN, SYNACK and ACK),
the received skb will be available to the bpf prog during the callback
in bpf_skops_established() introduced in the previous patch and
in the bpf_skops_write_hdr_opt() that will be added in the
next patch.
Calling bpf prog to parse header is controlled by two new flags in
tp->bpf_sock_ops_cb_flags:
BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG and
BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG.
When BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG is set,
the bpf prog will only be called when there is unknown
option in the TCP header.
When BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG is set,
the bpf prog will be called on all received TCP header.
This function is half implemented to highlight the changes in
TCP stack. The actual codes preparing the bpf running context and
invoking the bpf prog will be added in the later patch with other
necessary bpf pieces.
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:39 +0000 (12:00 -0700)]
bpf: tcp: Add bpf_skops_established()
In tcp_init_transfer(), it currently calls the bpf prog to give it a
chance to handle the just "ESTABLISHED" event (e.g. do setsockopt
on the newly established sk). Right now, it is done by calling the
general purpose tcp_call_bpf().
In the later patch, it also needs to pass the just-received skb which
concludes the 3 way handshake. E.g. the SYNACK received at the active side.
The bpf prog can then learn some specific header options written by the
peer's bpf-prog and potentially do setsockopt on the newly established sk.
Thus, instead of reusing the general purpose tcp_call_bpf(), a new function
bpf_skops_established() is added to allow passing the "skb" to the bpf
prog. The actual skb passing from bpf_skops_established() to the bpf prog
will happen together in a later patch which has the necessary bpf pieces.
A "skb" arg is also added to tcp_init_transfer() such that
it can then be passed to bpf_skops_established().
Calling the new bpf_skops_established() instead of tcp_call_bpf()
should be a noop in this patch.
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:33 +0000 (12:00 -0700)]
tcp: Add saw_unknown to struct tcp_options_received
In a later patch, the bpf prog only wants to be called to handle
a header option if that particular header option cannot be handled by
the kernel. This unknown option could be written by the peer's bpf-prog.
It could also be a new standard option that the running kernel does not
support it while a bpf-prog can handle it.
This patch adds a "saw_unknown" bit to "struct tcp_options_received"
and it uses an existing one byte hole to do that. "saw_unknown" will
be set in tcp_parse_options() if it sees an option that the kernel
cannot handle.
Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200820190033.2884430-1-kafai@fb.com
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:27 +0000 (12:00 -0700)]
tcp: bpf: Add TCP_BPF_RTO_MIN for bpf_setsockopt
This patch adds bpf_setsockopt(TCP_BPF_RTO_MIN) to allow bpf prog
to set the min rto of a connection. It could be used together
with the earlier patch which has added bpf_setsockopt(TCP_BPF_DELACK_MAX).
A later selftest patch will communicate the max delay ack in a
bpf tcp header option and then the receiving side can use
bpf_setsockopt(TCP_BPF_RTO_MIN) to set a shorter rto.
Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200820190027.2884170-1-kafai@fb.com
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:21 +0000 (12:00 -0700)]
tcp: bpf: Add TCP_BPF_DELACK_MAX setsockopt
This change is mostly from an internal patch and adapts it from sysctl
config to the bpf_setsockopt setup.
The bpf_prog can set the max delay ack by using
bpf_setsockopt(TCP_BPF_DELACK_MAX). This max delay ack can be communicated
to its peer through bpf header option. The receiving peer can then use
this max delay ack and set a potentially lower rto by using
bpf_setsockopt(TCP_BPF_RTO_MIN) which will be introduced
in the next patch.
Another later selftest patch will also use it like the above to show
how to write and parse bpf tcp header option.
Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200820190021.2884000-1-kafai@fb.com
Martin KaFai Lau [Thu, 20 Aug 2020 19:00:14 +0000 (12:00 -0700)]
tcp: Use a struct to represent a saved_syn
The TCP_SAVE_SYN has both the network header and tcp header.
The total length of the saved syn packet is currently stored in
the first 4 bytes (u32) of an array and the actual packet data is
stored after that.
A later patch will add a bpf helper that allows to get the tcp header
alone from the saved syn without the network header. It will be more
convenient to have a direct offset to a specific header instead of
re-parsing it. This requires to separately store the network hdrlen.
The total header length (i.e. network + tcp) is still needed for the
current usage in getsockopt. Although this total length can be obtained
by looking into the tcphdr and then get the (th->doff << 2), this patch
chooses to directly store the tcp hdrlen in the second four bytes of
this newly created "struct saved_syn". By using a new struct, it can
give a readable name to each individual header length.
Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200820190014.2883694-1-kafai@fb.com
Andrii Nakryiko [Thu, 20 Aug 2020 23:12:39 +0000 (16:12 -0700)]
libbpf: Normalize and improve logging across few functions
Make libbpf logs follow similar pattern and provide more context like section
name or program name, where appropriate. Also, add BPF_INSN_SZ constant and
use it throughout to clean up code a little bit. This commit doesn't have any
functional changes and just removes some code changes out of the way before
bigger refactoring in libbpf internals.
Andrii Nakryiko [Thu, 20 Aug 2020 23:12:38 +0000 (16:12 -0700)]
libbpf: Skip well-known ELF sections when iterating ELF
Skip and don't log ELF sections that libbpf knows about and ignores during ELF
processing. This allows to not unnecessarily log details about those ELF
sections and cleans up libbpf debug log. Ignored sections include DWARF data,
string table, empty .text section and few special (e.g., .llvm_addrsig)
useless sections.
With such ELF sections out of the way, log unrecognized ELF sections at
pr_info level to increase visibility.
Andrii Nakryiko [Thu, 20 Aug 2020 23:12:36 +0000 (16:12 -0700)]
libbpf: Factor out common ELF operations and improve logging
Factor out common ELF operations done throughout the libbpf. This simplifies
usage across multiple places in libbpf, as well as hide error reporting from
higher-level functions and make error logging more consistent.
Andrii Nakryiko [Thu, 20 Aug 2020 23:12:35 +0000 (16:12 -0700)]
selftests/bpf: BPF object files should depend only on libbpf headers
There is no need to re-build BPF object files if any of the sources of libbpf
change. So record more precise dependency only on libbpf/bpf_*.h headers. This
eliminates unnecessary re-builds.
====================
We're currently building a control plane for our BPF socket dispatch
work. As part of that, we have a need to create a copy of an existing
sockhash, to allow us to change the keys. I previously proposed allowing
privileged userspace to look up sockets, which doesn't work due to
security concerns (see [1]).
In follow up discussions during BPF office hours we identified bpf_iter
as a possible solution: instead of accessing sockets from user space
we can iterate the source sockhash, and insert the values into a new
map. Enabling this requires two pieces: the ability to iterate
sockmap and sockhash, as well as being able to call map_update_elem
from BPF.
This patch set implements the latter: it's now possible to update
sockmap from BPF context. As a next step, we can implement bpf_iter
for sockmap.
===
I've done some more fixups, and audited the safe contexts more
thoroughly. As a result I'm removing CGROUP_SKB, SK_MSG and SK_SKB
for now.
Changes in v3:
- Use CHECK as much as possible (Yonghong)
- Reject ARG_PTR_TO_MAP_VALUE_OR_NULL for sockmap (Yonghong)
- Remove CGROUP_SKB, SK_MSG, SK_SKB from safe contexts
- Test that the verifier rejects update from unsafe context
Changes in v2:
- Fix warning in patch #2 (Jakub K)
- Renamed override_map_arg_type (John)
- Only allow updating sockmap from known safe contexts (John)
- Use __s64 for sockmap updates from user space (Yonghong)
- Various small test fixes around test macros and such (Yonghong)
Lorenz Bauer [Fri, 21 Aug 2020 10:29:48 +0000 (11:29 +0100)]
selftests: bpf: Test sockmap update from BPF
Add a test which copies a socket from a sockmap into another sockmap
or sockhash. This excercises bpf_map_update_elem support from BPF
context. Compare the socket cookies from source and destination to
ensure that the copy succeeded.
Also check that the verifier rejects map_update from unsafe contexts.
Lorenz Bauer [Fri, 21 Aug 2020 10:29:47 +0000 (11:29 +0100)]
bpf: sockmap: Allow update from BPF
Allow calling bpf_map_update_elem on sockmap and sockhash from a BPF
context. The synchronization required for this is a bit fiddly: we
need to prevent the socket from changing its state while we add it
to the sockmap, since we rely on getting a callback via
sk_prot->unhash. However, we can't just lock_sock like in
sock_map_sk_acquire because that might sleep. So instead we disable
softirq processing and use bh_lock_sock to prevent further
modification.
Yet, this is still not enough. BPF can be called in contexts where
the current CPU might have locked a socket. If the BPF can get
a hold of such a socket, inserting it into a sockmap would lead to
a deadlock. One straight forward example are sock_ops programs that
have ctx->sk, but the same problem exists for kprobes, etc.
We deal with this by allowing sockmap updates only from known safe
contexts. Improper usage is rejected by the verifier.
I've audited the enabled contexts to make sure they can't run in
a locked context. It's possible that CGROUP_SKB and others are
safe as well, but the auditing here is much more difficult. In
any case, we can extend the safe contexts when the need arises.
Lorenz Bauer [Fri, 21 Aug 2020 10:29:46 +0000 (11:29 +0100)]
bpf: Override the meaning of ARG_PTR_TO_MAP_VALUE for sockmap and sockhash
The verifier assumes that map values are simple blobs of memory, and
therefore treats ARG_PTR_TO_MAP_VALUE, etc. as such. However, there are
map types where this isn't true. For example, sockmap and sockhash store
sockets. In general this isn't a big problem: we can just
write helpers that explicitly requests PTR_TO_SOCKET instead of
ARG_PTR_TO_MAP_VALUE.
The one exception are the standard map helpers like map_update_elem,
map_lookup_elem, etc. Here it would be nice we could overload the
function prototype for different kinds of maps. Unfortunately, this
isn't entirely straight forward:
We only know the type of the map once we have resolved meta->map_ptr
in check_func_arg. This means we can't swap out the prototype
in check_helper_call until we're half way through the function.
Instead, modify check_func_arg to treat ARG_PTR_TO_MAP_VALUE to
mean "the native type for the map" instead of "pointer to memory"
for sockmap and sockhash. This means we don't have to modify the
function prototype at all
Lorenz Bauer [Fri, 21 Aug 2020 10:29:45 +0000 (11:29 +0100)]
bpf: sockmap: Call sock_map_update_elem directly
Don't go via map->ops to call sock_map_update_elem, since we know
what function to call in bpf_map_update_value. Since we currently
don't allow calling map_update_elem from BPF context, we can remove
ops->map_update_elem and rename the function to sock_map_update_elem_sys.
Lorenz Bauer [Fri, 21 Aug 2020 10:29:43 +0000 (11:29 +0100)]
net: sk_msg: Simplify sk_psock initialization
Initializing psock->sk_proto and other saved callbacks is only
done in sk_psock_update_proto, after sk_psock_init has returned.
The logic for this is difficult to follow, and needlessly complex.
Instead, initialize psock->sk_proto whenever we allocate a new
psock. Additionally, assert the following invariants:
* The SK has no ULP: ULP does it's own finagling of sk->sk_prot
* sk_user_data is unused: we need it to store sk_psock
Protect our access to sk_user_data with sk_callback_lock, which
is what other users like reuseport arrays, etc. do.
The result is that an sk_psock is always fully initialized, and
that psock->sk_proto is always the "original" struct proto.
The latter allows us to use psock->sk_proto when initializing
IPv6 TCP / UDP callbacks for sockmap.
Andrii Nakryiko [Fri, 21 Aug 2020 16:59:27 +0000 (09:59 -0700)]
libbpf: Add perf_buffer APIs for better integration with outside epoll loop
Add a set of APIs to perf_buffer manage to allow applications to integrate
perf buffer polling into existing epoll-based infrastructure. One example is
applications using libevent already and wanting to plug perf_buffer polling,
instead of relying on perf_buffer__poll() and waste an extra thread to do it.
But perf_buffer is still extremely useful to set up and consume perf buffer
rings even for such use cases.
So to accomodate such new use cases, add three new APIs:
- perf_buffer__buffer_cnt() returns number of per-CPU buffers maintained by
given instance of perf_buffer manager;
- perf_buffer__buffer_fd() returns FD of perf_event corresponding to
a specified per-CPU buffer; this FD is then polled independently;
- perf_buffer__consume_buffer() consumes data from single per-CPU buffer,
identified by its slot index.
To support a simpler, but less efficient, way to integrate perf_buffer into
external polling logic, also expose underlying epoll FD through
perf_buffer__epoll_fd() API. It will need to be followed by
perf_buffer__poll(), wasting extra syscall, or perf_buffer__consume(), wasting
CPU to iterate buffers with no data. But could be simpler and more convenient
for some cases.
These APIs allow for great flexiblity, but do not sacrifice general usability
of perf_buffer.
Also exercise and check new APIs in perf_buffer selftest.
====================
"link" has been an important concept for bpf ecosystem to connect
bpf program with other properties. Currently, the information related
information can be queried from userspace through bpf command
BPF_LINK_GET_NEXT_ID, BPF_LINK_GET_FD_BY_ID and BPF_OBJ_GET_INFO_BY_FD.
The information is also available by "cating" /proc/<pid>/fdinfo/<link_fd>.
Raw_tracepoint, tracing, cgroup, netns and xdp links are already
supported in the kernel and bpftool.
This patch added support for bpf iterator. Patch #1 added generic support
for link querying interface. Patch #2 implemented callback functions
for map element bpf iterators. Patch #3 added bpftool support.
Changelogs:
v3 -> v4:
. return target specific link_info even if target_name buffer
is empty. (Andrii)
v2 -> v3:
. remove extra '\t' when fdinfo prints map_id to make parsing
consistent. (Andrii)
v1 -> v2:
. fix checkpatch.pl warnings. (Jakub)
====================
Yonghong Song [Fri, 21 Aug 2020 18:44:20 +0000 (11:44 -0700)]
bpftool: Implement link_query for bpf iterators
The link query for bpf iterators is implemented.
Besides being shown to the user what bpf iterator
the link represents, the target_name is also used
to filter out what additional information should be
printed out, e.g., whether map_id should be shown or not.
The following is an example of bpf_iter link dump,
plain output or pretty output.
Yonghong Song [Fri, 21 Aug 2020 18:44:19 +0000 (11:44 -0700)]
bpf: Implement link_query callbacks in map element iterators
For bpf_map_elem and bpf_sk_local_storage bpf iterators,
additional map_id should be shown for fdinfo and
userspace query. For example, the following is for
a bpf_map_elem iterator.
$ cat /proc/1753/fdinfo/9
pos: 0
flags: 02000000
mnt_id: 14
link_type: iter
link_id: 34
prog_tag: 104be6d3fe45e6aa
prog_id: 173
target_name: bpf_map_elem
map_id: 127
Yonghong Song [Fri, 21 Aug 2020 18:44:18 +0000 (11:44 -0700)]
bpf: Implement link_query for bpf iterators
This patch implemented bpf_link callback functions
show_fdinfo and fill_link_info to support link_query
interface.
The general interface for show_fdinfo and fill_link_info
will print/fill the target_name. Each targets can
register show_fdinfo and fill_link_info callbacks
to print/fill more target specific information.
For example, the below is a fdinfo result for a bpf
task iterator.
$ cat /proc/1749/fdinfo/7
pos: 0
flags: 02000000
mnt_id: 14
link_type: iter
link_id: 11
prog_tag: 990e1f8152f7e54f
prog_id: 59
target_name: task
Andrii Nakryiko [Thu, 20 Aug 2020 06:14:11 +0000 (23:14 -0700)]
selftests/bpf: List newest Clang built-ins needed for some CO-RE selftests
Record which built-ins are optional and needed for some of recent BPF CO-RE
subtests. Document Clang diff that fixed corner-case issue with
__builtin_btf_type_id().
Andrii Nakryiko [Thu, 20 Aug 2020 06:14:09 +0000 (23:14 -0700)]
libbpf: Fix libbpf build on compilers missing __builtin_mul_overflow
GCC compilers older than version 5 don't support __builtin_mul_overflow yet.
Given GCC 4.9 is the minimal supported compiler for building kernel and the
fact that libbpf is a dependency of resolve_btfids, which is dependency of
CONFIG_DEBUG_INFO_BTF=y, this needs to be handled. This patch fixes the issue
by falling back to slower detection of integer overflow in such cases.
Fixes: 029258d7b228 ("libbpf: Remove any use of reallocarray() in libbpf") Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20200820061411.1755905-2-andriin@fb.com
Andrii Nakryiko [Thu, 20 Aug 2020 06:14:08 +0000 (23:14 -0700)]
libbpf: Fix detection of BPF helper call instruction
BPF_CALL | BPF_JMP32 is explicitly not allowed by verifier for BPF helper
calls, so don't detect it as a valid call. Also drop the check on func_id
pointer, as it's currently always non-null.
Fixes: 109cea5a594f ("libbpf: Sanitize BPF program code for bpf_probe_read_{kernel, user}[_str]") Reported-by: Yonghong Song <yhs@fb.com> Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20200820061411.1755905-1-andriin@fb.com
Daniel Borkmann [Thu, 20 Aug 2020 14:02:36 +0000 (16:02 +0200)]
Merge branch 'bpf-umd-debug'
Alexei Starovoitov says:
====================
This patch set is the first real user of user mode driver facility. The
general use case for user mode driver is to ship vmlinux with preloaded BPF
programs. In this particular case the user mode driver populates bpffs instance
with two BPF iterators. In several months BPF_LSM project would need to preload
the kernel with its own set of BPF programs and attach to LSM hooks instead of
bpffs. BPF iterators and BPF_LSM are unstable from uapi perspective. They are
tracing based and peek into arbitrary kernel data structures. One can question
why a kernel module cannot embed BPF programs inside. The reason is that libbpf
is necessary to load them. First libbpf loads BPF Type Format, then creates BPF
maps, populates them. Then it relocates code sections inside BPF programs,
loads BPF programs, and finally attaches them to events. Theoretically libbpf
can be rewritten to work in the kernel, but that is massive undertaking. The
maintenance of in-kernel libbpf and user space libbpf would be another
challenge. Another obstacle to embedding BPF programs into kernel module is
sys_bpf api. Loading of programs, BTF, maps goes through the verifier. It
validates and optimizes the code. It's possible to provide in-kernel api to all
of sys_bpf commands (load progs, create maps, update maps, load BTF, etc), but
that is huge amount of work and forever maintenance headache.
Hence the decision is to ship vmlinux with user mode drivers that load
BPF programs. Just like kernel modules extend vmlinux BPF programs
are safe extensions of the kernel and some of them need to ship with vmlinux.
This patch set adds a kernel module with user mode driver that populates bpffs
with two BPF iterators.
The user mode driver will load BPF Type Formats, create BPF maps, populate BPF
maps, load two BPF programs, attach them to BPF iterators, and finally send two
bpf_link IDs back to the kernel.
The kernel will pin two bpf_links into newly mounted bpffs instance under
names "progs.debug" and "maps.debug". These two files become human readable.
The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about
all BPF programs currently loaded in the system. This information is unstable
and will change from kernel to kernel.
In some sence this output is similar to 'bpftool prog show' that is using
stable api to retreive information about BPF programs. The BPF subsytems grows
quickly and there is always demand to show as much info about BPF things as
possible. But we cannot expose all that info via stable uapi of bpf syscall,
since the details change so much. Right now a BPF program can be attached to
only one other BPF program. Folks are working on patches to enable
multi-attach, but for debugging it's necessary to see the current state. There
is no uapi for that, but above output shows it:
37 new_get_skb_ifindex get_skb_ifindex test_pkt_access
38 new_get_constant get_constant test_pkt_access
[1] [2] [3]
[1] is the full name of BPF prog from BTF.
[2] is the name of function inside target BPF prog.
[3] is the name of target BPF prog.
[2] and [3] are not exposed via uapi, since they will change from single to
multi soon. There are many other cases where bpf internals are useful for
debugging, but shouldn't be exposed via uapi due to high rate of changes.
systemd mounts /sys/fs/bpf at the start, so this kernel module with user mode
driver needs to be available early. BPF_LSM most likely would need to preload
BPF programs even earlier.
Few interesting observations:
- though bpffs comes with two human readble files "progs.debug" and
"maps.debug" they can be removed. 'rm -f /sys/fs/bpf/progs.debug' will remove
bpf_link and kernel will automatically unload corresponding BPF progs, maps,
BTFs. In the future '-o remount' will be able to restore them. This is not
implemented yet.
- 'ps aux|grep bpf_preload' shows nothing. User mode driver loaded BPF
iterators and exited. Nothing is lingering in user space at this point.
- We can consider giving 0644 permissions to "progs.debug" and "maps.debug"
to allow unprivileged users see BPF things loaded in the system.
We cannot do so with "bpftool prog show", since it's using cap_sys_admin
parts of bpf syscall.
- The functionality split between core kernel, bpf_preload kernel module and
user mode driver is very similar to bpfilter style of interaction.
- Similar BPF iterators can be used as unstable extensions to /proc.
Like mounting /proc can prepopolate some subdirectory in there with
a BPF iterator that will print QUIC sockets instead of tcp and udp.
Changelog:
v5->v6:
- refactored Makefiles with Andrii's help
- switched to explicit $(MAKE) style
- switched to userldlibs instead of userldflags
- fixed build issue with libbpf Makefile due to invocation from kbuild
- fixed menuconfig order as spotted by Daniel
- introduced CONFIG_USERMODE_DRIVER bool that is selected by bpfilter and bpf_preload
v4->v5:
- addressed Song and Andrii feedback. s/pages/max_entries/
v3->v4:
- took THIS_MODULE in patch 3 as suggested by Daniel to simplify the code.
- converted BPF iterator to use BTF (when available) to print full BPF program name
instead of 16-byte truncated version.
This is something I've been using drgn scripts for.
Take a look at get_name() in iterators.bpf.c to see how short it is comparing
to what user space bpftool would have to do to print the same full name:
. get prog info via obj_info_by_fd
. do get_fd_by_id from info->btf_id
. fetch potentially large BTF of the program from the kernel
. parse that BTF in user space to figure out all type boundaries and string section
. read info->func_info to get btf_id of func_proto from there
. find that btf_id in the parsed BTF
That's quite a bit work for bpftool comparing to few lines in get_name().
I guess would be good to make bpftool do this info extraction anyway.
While doing this BTF reading in the kernel realized that the verifier is not smart
enough to follow double pointers (added to my todo list), otherwise get_name()
would have been even shorter.
v1->v2:
- changed names to 'progs.debug' and 'maps.debug' to hopefully better indicate
instability of the text output. Having dot in the name also guarantees
that these special files will not conflict with normal bpf objects pinned
in bpffs, since dot is disallowed for normal pins.
- instead of hard coding link_name in the core bpf moved into UMD.
- cleanedup error handling.
- addressed review comments from Yonghong and Andrii.
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The user mode driver will load BPF Type Formats, create BPF maps, populate BPF
maps, load two BPF programs, attach them to BPF iterators, and finally send two
bpf_link IDs back to the kernel.
The kernel will pin two bpf_links into newly mounted bpffs instance under
names "progs.debug" and "maps.debug". These two files become human readable.
The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about
all BPF programs currently loaded in the system. This information is unstable
and will change from kernel to kernel as ".debug" suffix conveys.
bpf: Add BPF program and map iterators as built-in BPF programs.
The program and map iterators work similar to seq_file-s.
Once the program is pinned in bpffs it can be read with "cat" tool
to print human readable output. In this case about BPF programs and maps.
For example:
$ cat /sys/fs/bpf/progs.debug
id name attached
5 dump_bpf_map bpf_iter_bpf_map
6 dump_bpf_prog bpf_iter_bpf_prog
$ cat /sys/fs/bpf/maps.debug
id name max_entries
3 iterator.rodata 1
To avoid kernel build dependency on clang 10 separate bpf skeleton generation
into manual "make" step and instead check-in generated .skel.h into git.
Unlike 'bpftool prog show' in-kernel BTF name is used (when available)
to print full name of BPF program instead of 16-byte truncated name.
====================
This patch set adds libbpf support for two new classes of CO-RE relocations:
type-based (TYPE_EXISTS/TYPE_SIZE/TYPE_ID_LOCAL/TYPE_ID_TARGET) and enum
value-vased (ENUMVAL_EXISTS/ENUMVAL_VALUE):
- TYPE_EXISTS allows to detect presence in kernel BTF of a locally-recorded
BTF type. Useful for feature detection (new functionality often comes with
new internal kernel types), as well as handling type renames and bigger
refactorings.
- TYPE_SIZE allows to get the real size (in bytes) of a specified kernel
type. Useful for dumping internal structure as-is through perfbuf or
ringbuf.
- TYPE_ID_LOCAL/TYPE_ID_TARGET allow to capture BTF type ID of a BTF type in
program's BTF or kernel BTF, respectively. These could be used for
high-performance and space-efficient generic data dumping/logging by
relying on small and cheap BTF type ID as a data layout descriptor, for
post-processing on user-space side.
- ENUMVAL_EXISTS can be used for detecting the presence of enumerator value
in kernel's enum type. Most direct application is to detect BPF helper
support in kernel.
- ENUMVAL_VALUE allows to relocate real integer value of kernel enumerator
value, which is subject to change (e.g., always a potential issue for
internal, non-UAPI, kernel enums).
I've indicated potential applications for these relocations, but relocations
themselves are generic and unassuming and are designed to work correctly even
in unintended applications. Furthermore, relocated values become constants,
known to the verifier and could and would be used for dead branch code
detection and elimination. This makes them ideal to do all sorts of feature
detection and guarding functionality that's not available on some older (but
still supported by BPF program) kernels, while having to compile and maintain
one unified source code.
Selftests are added for all the new features. Selftests utilizing new Clang
built-ins are designed such that they will compile with older Clangs and will
be skipped during test runs. So this shouldn't cause any build and test
failures on systems with slightly outdated Clang compiler.
LLVM patches adding these relocation in Clang:
- __builtin_btf_type_id() ([0], [1], [2]);
- __builtin_preserve_type_info(), __builtin_preserve_enum_value() ([3], [4]).
Andrii Nakryiko [Wed, 19 Aug 2020 19:45:19 +0000 (12:45 -0700)]
selftests/bpf: Add tests for ENUMVAL_EXISTS/ENUMVAL_VALUE relocations
Add tests validating existence and value relocations for enum value-based
relocations. If __builtin_preserve_enum_value() built-in is not supported,
skip tests.
Implement two relocations of a new enumerator value-based CO-RE relocation
kind: ENUMVAL_EXISTS and ENUMVAL_VALUE.
First, ENUMVAL_EXISTS, allows to detect the presence of a named enumerator
value in the target (kernel) BTF. This is useful to do BPF helper/map/program
type support detection from BPF program side. bpf_core_enum_value_exists()
macro helper is provided to simplify built-in usage.
Second, ENUMVAL_VALUE, allows to capture enumerator integer value and relocate
it according to the target BTF, if it changes. This is useful to have
a guarantee against intentional or accidental re-ordering/re-numbering of some
of the internal (non-UAPI) enumerations, where kernel developers don't care
about UAPI backwards compatiblity concerns. bpf_core_enum_value() allows to
capture this succinctly and use correct enum values in code.
LLVM uses ldimm64 instruction to capture enumerator value-based relocations,
so add support for ldimm64 instruction patching as well.
Andrii Nakryiko [Wed, 19 Aug 2020 19:45:17 +0000 (12:45 -0700)]
selftests/bpf: Add CO-RE relo test for TYPE_ID_LOCAL/TYPE_ID_TARGET
Add tests for BTF type ID relocations. To allow testing this, enhance
core_relo.c test runner to allow dynamic initialization of test inputs.
If Clang doesn't have necessary support for new functionality, test is
skipped.
Andrii Nakryiko [Wed, 19 Aug 2020 19:45:15 +0000 (12:45 -0700)]
libbpf: Implement type-based CO-RE relocations support
Implement support for TYPE_EXISTS/TYPE_SIZE/TYPE_ID_LOCAL/TYPE_ID_REMOTE
relocations. These are examples of type-based relocations, as opposed to
field-based relocations supported already. The difference is that they are
calculating relocation values based on the type itself, not a field within
a struct/union.
Type-based relos have slightly different semantics when matching local types
to kernel target types, see comments in bpf_core_types_are_compat() for
details. Their behavior on failure to find target type in kernel BTF also
differs. Instead of "poisoning" relocatable instruction and failing load
subsequently in kernel, they return 0 (which is rarely a valid return result,
so user BPF code can use that to detect success/failure of the relocation and
deal with it without extra "guarding" relocations). Also, it's always possible
to check existence of the type in target kernel with TYPE_EXISTS relocation,
similarly to a field-based FIELD_EXISTS.
TYPE_ID_LOCAL relocation is a bit special in that it always succeeds (barring
any libbpf/Clang bugs) and resolved to BTF ID using **local** BTF info of BPF
program itself. Tests in subsequent patches demonstrate the usage and
semantics of new relocations.
====================
Get rid of two feature detectors: reallocarray and libelf-mmap. Optional
feature detections complicate libbpf Makefile and cause more troubles for
various applications that want to integrate libbpf as part of their build.
Patch #1 replaces all reallocarray() uses into libbpf-internal reallocarray()
implementation. Patches #2 and #3 makes sure we won't re-introduce
reallocarray() accidentally. Patch #2 also removes last use of
libbpf_internal.h header inside bpftool. There is still nlattr.h that's used
by both libbpf and bpftool, but that's left for a follow up patch to split.
Patch #4 removed libelf-mmap feature detector and all its uses, as it's
trivial to handle missing mmap support in libbpf, the way objtool has been
doing it for a while.
v1->v2 and v2->v3:
- rebase to latest bpf-next (Alexei).
====================
It's trivial to handle missing ELF_C_MMAP_READ support in libelf the way that
objtool has solved it in
("774bec3fddcc objtool: Add fallback from ELF_C_READ_MMAP to ELF_C_READ").
So instead of having an entire feature detector for that, just do what objtool
does for perf and libbpf. And keep their Makefiles a bit simpler.
Andrii Nakryiko [Wed, 19 Aug 2020 01:36:06 +0000 (18:36 -0700)]
libbpf: Centralize poisoning and poison reallocarray()
Most of libbpf source files already include libbpf_internal.h, so it's a good
place to centralize identifier poisoning. So move kernel integer type
poisoning there. And also add reallocarray to a poison list to prevent
accidental use of it. libbpf_reallocarray() should be used universally
instead.
Andrii Nakryiko [Wed, 19 Aug 2020 01:36:05 +0000 (18:36 -0700)]
tools/bpftool: Remove libbpf_internal.h usage in bpftool
Most netlink-related functions were unique to bpftool usage, so I moved them
into net.c. Few functions are still used by both bpftool and libbpf itself
internally, so I've copy-pasted them (libbpf_nl_get_link,
libbpf_netlink_open). It's a bit of duplication of code, but better separation
of libbpf as a library with public API and bpftool, relying on unexposed
functions in libbpf.
Andrii Nakryiko [Wed, 19 Aug 2020 01:36:04 +0000 (18:36 -0700)]
libbpf: Remove any use of reallocarray() in libbpf
Re-implement glibc's reallocarray() for libbpf internal-only use.
reallocarray(), unfortunately, is not available in all versions of glibc, so
requires extra feature detection and using reallocarray() stub from
<tools/libc_compat.h> and COMPAT_NEED_REALLOCARRAY. All this complicates build
of libbpf unnecessarily and is just a maintenance burden. Instead, it's
trivial to implement libbpf-specific internal version and use it throughout
libbpf.
Which is what this patch does, along with converting some realloc() uses that
should really have been reallocarray() in the first place.
Andrii Nakryiko [Tue, 18 Aug 2020 22:39:15 +0000 (15:39 -0700)]
libbpf: Improve relocation ambiguity detection
Split the instruction patching logic into relocation value calculation and
application of relocation to instruction. Using this, evaluate relocation
against each matching candidate and validate that all candidates agree on
relocated value. If not, report ambiguity and fail load.
This logic is necessary to avoid dangerous (however unlikely) accidental match
against two incompatible candidate types. Without this change, libbpf will
pick a random type as *the* candidate and apply potentially invalid
relocation.
Andrii Nakryiko [Tue, 18 Aug 2020 22:39:14 +0000 (15:39 -0700)]
libbpf: Clean up and improve CO-RE reloc logging
Add logging of local/target type kind (struct/union/typedef/etc). Preserve
unresolved root type ID (for cases of typedef). Improve the format of CO-RE
reloc spec output format to contain only relevant and succinct info.
====================
This patch set refactors libbpf feature probing to be done lazily on as-needed
basis, instead of proactively testing all possible features libbpf knows
about. This allows to scale such detections and mitigations better, without
issuing unnecessary syscalls on each bpf_object__load() call. It's also now
memoized globally, instead of per-bpf_object.
Building on that, libbpf will now detect availability of
bpf_probe_read_kernel() helper (which means also -user and -str variants), and
will sanitize BPF program code by replacing such references to generic
variants (bpf_probe_read[_str]()). This allows to migrate all BPF programs
into proper -kernel/-user probing helpers, without the fear of breaking them
for old kernels.
With that, update BPF_CORE_READ() and related macros to use
bpf_probe_read_kernel(), as it doesn't make much sense to do CO-RE relocations
against user-space types. And the only class of cases in which BPF program
might read kernel type from user-space are UAPI data structures which by
definition are fixed in their memory layout and don't need relocating. This is
exemplified by test_vmlinux test, which is fixed as part of this patch set as
well. BPF_CORE_READ() is useful for chainingg bpf_probe_read_{kernel,user}()
calls together even without relocation, so we might add user-space variants,
if there is a need.
While at making libbpf more useful for older kernels, also improve handling of
a complete lack of BTF support in kernel by not even attempting to load BTF
info into kernel. This eliminates annoying warning about lack of BTF support
in the kernel and map creation retry without BTF. If user is using features
that require kernel BTF support, it will still fail, of course.
====================
Andrii Nakryiko [Tue, 18 Aug 2020 21:33:55 +0000 (14:33 -0700)]
libbpf: Switch tracing and CO-RE helper macros to bpf_probe_read_kernel()
Now that libbpf can automatically fallback to bpf_probe_read() on old kernels
not yet supporting bpf_probe_read_kernel(), switch libbpf BPF-side helper
macros to use appropriate BPF helper for reading kernel data.
Andrii Nakryiko [Tue, 18 Aug 2020 21:33:53 +0000 (14:33 -0700)]
libbpf: Sanitize BPF program code for bpf_probe_read_{kernel, user}[_str]
Add BPF program code sanitization pass, replacing calls to BPF
bpf_probe_read_{kernel,user}[_str]() helpers with bpf_probe_read[_str](), if
libbpf detects that kernel doesn't support new variants.
Andrii Nakryiko [Tue, 18 Aug 2020 21:33:51 +0000 (14:33 -0700)]
libbpf: Make kernel feature probing lazy
Turn libbpf's kernel feature probing into lazily-performed checks. This allows
to skip performing unnecessary feature checks, if a given BPF application
doesn't rely on a particular kernel feature. As we grow number of feature
probes, libbpf might perform less unnecessary syscalls and scale better with
number of feature probes long-term.
By decoupling feature checks from bpf_object, it's also possible to perform
feature probing from libbpf static helpers and low-level APIs, if necessary.
Daniel T. Lee [Tue, 18 Aug 2020 05:16:41 +0000 (14:16 +0900)]
samples: bpf: Fix broken bpf programs due to removed symbol
>From commit f1394b798814 ("block: mark blk_account_io_completion
static") symbol blk_account_io_completion() has been marked as static,
which makes it no longer possible to attach kprobe to this event.
Currently, there are broken samples due to this reason.
As a solution to this, attach kprobe events to blk_account_io_done()
to modify them to perform the same behavior as before.
====================
netlink: allow NLA_BINARY length range validation
In quite a few places (perhaps particularly in wireless) we need to
validation an NLA_BINARY attribute with both a minimum and a maximum
length. Currently, we can do either of the two, but not both, given
that we have NLA_MIN_LEN (minimum length) and NLA_BINARY (maximum).
Extend the range mechanisms that we use for integer validation to
apply to NLA_BINARY as well.
After converting everything to use NLA_POLICY_MIN_LEN() we can thus
get rid of the NLA_MIN_LEN type since that's now a special case of
NLA_BINARY with a minimum length validation. Similarly, NLA_EXACT_LEN
can be specified using NLA_POLICY_EXACT_LEN() and also maps to the
new NLA_BINARY validation (min == max == desired length).
Finally, NLA_POLICY_EXACT_LEN_WARN() also gets to be a somewhat
special case of this.
I haven't included the patch here now that converts nl82011 to use
this because it doesn't apply without another cleanup patch, but
we can remove a number of hand-coded min/max length checks and get
better error messages from the general validation code while doing
that.
As I had originally built the netlink policy export to userspace in
a way that has min/max length for NLA_BINARY (for the types that we
used to call NLA_MIN_LEN, NLA_BINARY and NLA_EXACT_LEN) anyway, it
doesn't really change anything there except that now there's a chance
that userspace sees min length < max length, which previously wasn't
possible.
v2:
* fix the min<max comment to correctly say min<=max
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Johannes Berg [Tue, 18 Aug 2020 08:17:33 +0000 (10:17 +0200)]
netlink: make NLA_BINARY validation more flexible
Add range validation for NLA_BINARY, allowing validation of any
combination of combination minimum or maximum lengths, using the
existing NLA_POLICY_RANGE()/NLA_POLICY_FULL_RANGE() macros, just
like for integers where the value is checked.
Also make NLA_POLICY_EXACT_LEN(), NLA_POLICY_EXACT_LEN_WARN()
and NLA_POLICY_MIN_LEN() special cases of this, removing the old
types NLA_EXACT_LEN and NLA_MIN_LEN.
This allows us to save some code where both minimum and maximum
lengths are requires, currently the policy only allows maximum
(NLA_BINARY), minimum (NLA_MIN_LEN) or exact (NLA_EXACT_LEN), so
a range of lengths cannot be accepted and must be checked by the
code that consumes the attributes later.
Also, this allows advertising the correct ranges in the policy
export to userspace. Here, NLA_MIN_LEN and NLA_EXACT_LEN already
were special cases of NLA_BINARY with min and min/max length
respectively.
Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Johannes Berg [Tue, 18 Aug 2020 08:17:31 +0000 (10:17 +0200)]
netlink: consistently use NLA_POLICY_EXACT_LEN()
Change places that open-code NLA_POLICY_EXACT_LEN() to
use the macro instead, giving us flexibility in how we
handle the details of the macro.
Signed-off-by: Johannes Berg <johannes.berg@intel.com> Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net> Signed-off-by: David S. Miller <davem@davemloft.net>
projects / mirror_ubuntu-kernels.git / log