rseq: Use __u64 for rseq_cs fields, validate user inputs

Change the rseq ABI so rseq_cs start_ip, post_commit_offset and abort_ip
fields are seen as 64-bit fields by both 32-bit and 64-bit kernels rather
that ignoring the 32 upper bits on 32-bit kernels. This ensures we have a
consistent behavior for a 32-bit binary executed on 32-bit kernels and in
compat mode on 64-bit kernels.

Validating the value of abort_ip field to be below TASK_SIZE ensures the
kernel don't return to an invalid address when returning to userspace
after an abort. I don't fully trust each architecture code to consistently
deal with invalid return addresses.

Validating the value of the start_ip and post_commit_offset fields
prevents overflow on arithmetic performed on those values, used to
check whether abort_ip is within the rseq critical section.

If validation fails, the process is killed with a segmentation fault.

When the signature encountered before abort_ip does not match the expected
signature, return -EINVAL rather than -EPERM to be consistent with other
input validation return codes from rseq_get_rseq_cs().

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Watson <davejwatson@fb.com>
Cc: Paul Turner <pjt@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Chris Lameter <cl@linux.com>
Cc: Ben Maurer <bmaurer@fb.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180709195155.7654-2-mathieu.desnoyers@efficios.com

diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index d620fa43756cab2685428861f31c27d9a59b2a39..519ad6e176d15baf147ed59c9529e6660f1847e0 100644 (file)
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -52,10 +52,10 @@ struct rseq_cs {
        __u32 version;
        /* enum rseq_cs_flags */
        __u32 flags;
-       LINUX_FIELD_u32_u64(start_ip);
+       __u64 start_ip;
        /* Offset from start_ip. */
-       LINUX_FIELD_u32_u64(post_commit_offset);
-       LINUX_FIELD_u32_u64(abort_ip);
+       __u64 post_commit_offset;
+       __u64 abort_ip;
 } __attribute__((aligned(4 * sizeof(__u64))));
 
 /*

diff --git a/kernel/rseq.c b/kernel/rseq.c
index 22b6acf1ad6377b502e3a77b54939eec5d27d139..16b38c5342f9c98faad9cf7b2a8c526944c2f5de 100644 (file)
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -130,14 +130,20 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
        urseq_cs = (struct rseq_cs __user *)ptr;
        if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
                return -EFAULT;
-       if (rseq_cs->version > 0)
-               return -EINVAL;
 
+       if (rseq_cs->start_ip >= TASK_SIZE ||
+           rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
+           rseq_cs->abort_ip >= TASK_SIZE ||
+           rseq_cs->version > 0)
+               return -EINVAL;
+       /* Check for overflow. */
+       if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
+               return -EINVAL;
        /* Ensure that abort_ip is not in the critical section. */
        if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
                return -EINVAL;
 
-       usig = (u32 __user *)(rseq_cs->abort_ip - sizeof(u32));
+       usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
        ret = get_user(sig, usig);
        if (ret)
                return ret;
@@ -146,7 +152,7 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
                printk_ratelimited(KERN_WARNING
                        "Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
                        sig, current->rseq_sig, current->pid, usig);
-               return -EPERM;
+               return -EINVAL;
        }
        return 0;
 }