x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic()
authorJosh Poimboeuf <jpoimboe@redhat.com>
Thu, 4 May 2017 14:51:40 +0000 (09:51 -0500)
committerIngo Molnar <mingo@kernel.org>
Fri, 5 May 2017 05:59:24 +0000 (07:59 +0200)
commit42fc6c6cb1662ba2fa727dd01c9473c63be4e3b6
treebe27183342fdd3eea4f75d8b8645964fb0a81045
parentbfb8c6e495b9fc14c315e0f1550394b2137035b4
x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic()

Andrey Konovalov reported the following warning while fuzzing the kernel
with syzkaller:

  WARNING: kernel stack regs at ffff8800686869f8 in a.out:4933 has bad 'bp' value c3fc855a10167ec0

The unwinder dump revealed that RBP had a bad value when an interrupt
occurred in csum_partial_copy_generic().

That function saves RBP on the stack and then overwrites it, using it as
a scratch register.  That's problematic because it breaks stack traces
if an interrupt occurs in the middle of the function.

Replace the usage of RBP with another callee-saved register (R15) so
stack traces are no longer affected.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: linux-sctp@vger.kernel.org
Cc: netdev <netdev@vger.kernel.org>
Cc: syzkaller <syzkaller@googlegroups.com>
Link: http://lkml.kernel.org/r/4b03a961efda5ec9bfe46b7b9c9ad72d1efad343.1493909486.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/lib/csum-copy_64.S