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 <[email protected]>
Tested-by: Andrey Konovalov <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: David S . Miller <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Kostya Serebryany <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Marcelo Ricardo Leitner <[email protected]>
Cc: Neil Horman <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vlad Yasevich <[email protected]>
Cc: [email protected]
Cc: netdev <[email protected]>
Cc: syzkaller <[email protected]>
Link: http://lkml.kernel.org/r/4b03a961efda5ec9bfe46b7b9c9ad72d1efad343.1493909486.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions