cpu/speculation: Add 'mitigations=' cmdline option

Keeping track of the number of mitigations for all the CPU speculation
bugs has become overwhelming for many users.  It's getting more and more
complicated to decide which mitigations are needed for a given
architecture.  Complicating matters is the fact that each arch tends to
have its own custom way to mitigate the same vulnerability.

Most users fall into a few basic categories:

a) they want all mitigations off;

b) they want all reasonable mitigations on, with SMT enabled even if
   it's vulnerable; or

c) they want all reasonable mitigations on, with SMT disabled if
   vulnerable.

Define a set of curated, arch-independent options, each of which is an
aggregation of existing options:

- mitigations=off: Disable all mitigations.

- mitigations=auto: [default] Enable all the default mitigations, but
  leave SMT enabled, even if it's vulnerable.

- mitigations=auto,nosmt: Enable all the default mitigations, disabling
  SMT if needed by a mitigation.

Currently, these options are placeholders which don't actually do
anything.  They will be fleshed out in upcoming patches.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/b07a8ef9b7c5055c3a4637c87d07c296d5016fe0.1555085500.git.jpoimboe@redhat.com
CVE-2017-5715
CVE-2017-5754
CVE-2018-3639
CVE-2018-3620
CVE-2018-3646

(backported from commit 98af8452945c55652de68536afdde3b520fec429 https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git)
[tyhicks: Backport to 4.15:
 - Minor context differences since boot_cpu_state_init() uses per_cpu_ptr()
   instead of this_cpu_write()]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index eb2b0ca22bd120477564f8f73f769142a1db4740..811a524411a8a0f03d8a0a181926be02785d98bc 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2423,6 +2423,30 @@
                        in the "bleeding edge" mini2440 support kernel at
                        http://repo.or.cz/w/linux-2.6/mini2440.git
 
+       mitigations=
+                       Control optional mitigations for CPU vulnerabilities.
+                       This is a set of curated, arch-independent options, each
+                       of which is an aggregation of existing arch-specific
+                       options.
+
+                       off
+                               Disable all optional CPU mitigations.  This
+                               improves system performance, but it may also
+                               expose users to several CPU vulnerabilities.
+
+                       auto (default)
+                               Mitigate all CPU vulnerabilities, but leave SMT
+                               enabled, even if it's vulnerable.  This is for
+                               users who don't want to be surprised by SMT
+                               getting disabled across kernel upgrades, or who
+                               have other ways of avoiding SMT-based attacks.
+                               This is the default behavior.
+
+                       auto,nosmt
+                               Mitigate all CPU vulnerabilities, disabling SMT
+                               if needed.  This is for users who always want to
+                               be fully mitigated, even if it means losing SMT.
+
        mminit_loglevel=
                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
                        parameter allows control of the logging verbosity for

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index ea44bbaaf28f984df47faf3761af9eab15c87af0..785c716c9c30eff2fe975dcc3785f0d7ddc542cc 100644 (file)
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -189,4 +189,28 @@ static inline void cpu_smt_check_topology_early(void) { }
 static inline void cpu_smt_check_topology(void) { }
 #endif
 
+/*
+ * These are used for a global "mitigations=" cmdline option for toggling
+ * optional CPU mitigations.
+ */
+enum cpu_mitigations {
+       CPU_MITIGATIONS_OFF,
+       CPU_MITIGATIONS_AUTO,
+       CPU_MITIGATIONS_AUTO_NOSMT,
+};
+
+extern enum cpu_mitigations cpu_mitigations;
+
+/* mitigations=off */
+static inline bool cpu_mitigations_off(void)
+{
+       return cpu_mitigations == CPU_MITIGATIONS_OFF;
+}
+
+/* mitigations=auto,nosmt */
+static inline bool cpu_mitigations_auto_nosmt(void)
+{
+       return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
+}
+
 #endif /* _LINUX_CPU_H_ */

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 49b69217d8f75b08ff92d77fb7ad6e6223a7d36f..4c9fb05a71a005fc77260ebdd48c2c435292d14e 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2294,3 +2294,18 @@ void __init boot_cpu_state_init(void)
        per_cpu_ptr(&cpuhp_state, smp_processor_id())->booted_once = true;
        per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
 }
+
+enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO;
+
+static int __init mitigations_parse_cmdline(char *arg)
+{
+       if (!strcmp(arg, "off"))
+               cpu_mitigations = CPU_MITIGATIONS_OFF;
+       else if (!strcmp(arg, "auto"))
+               cpu_mitigations = CPU_MITIGATIONS_AUTO;
+       else if (!strcmp(arg, "auto,nosmt"))
+               cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
+
+       return 0;
+}
+early_param("mitigations", mitigations_parse_cmdline);