Commit 42fc6c6c authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

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: default avatarAndrey Konovalov <andreyknvl@google.com>
Tested-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: default avatarJosh 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: default avatarIngo Molnar <mingo@kernel.org>
parent bfb8c6e4
......@@ -55,7 +55,7 @@ ENTRY(csum_partial_copy_generic)
movq %r12, 3*8(%rsp)
movq %r14, 4*8(%rsp)
movq %r13, 5*8(%rsp)
movq %rbp, 6*8(%rsp)
movq %r15, 6*8(%rsp)
movq %r8, (%rsp)
movq %r9, 1*8(%rsp)
......@@ -74,7 +74,7 @@ ENTRY(csum_partial_copy_generic)
/* main loop. clear in 64 byte blocks */
/* r9: zero, r8: temp2, rbx: temp1, rax: sum, rcx: saved length */
/* r11: temp3, rdx: temp4, r12 loopcnt */
/* r10: temp5, rbp: temp6, r14 temp7, r13 temp8 */
/* r10: temp5, r15: temp6, r14 temp7, r13 temp8 */
.p2align 4
.Lloop:
source
......@@ -89,7 +89,7 @@ ENTRY(csum_partial_copy_generic)
source
movq 32(%rdi), %r10
source
movq 40(%rdi), %rbp
movq 40(%rdi), %r15
source
movq 48(%rdi), %r14
source
......@@ -103,7 +103,7 @@ ENTRY(csum_partial_copy_generic)
adcq %r11, %rax
adcq %rdx, %rax
adcq %r10, %rax
adcq %rbp, %rax
adcq %r15, %rax
adcq %r14, %rax
adcq %r13, %rax
......@@ -121,7 +121,7 @@ ENTRY(csum_partial_copy_generic)
dest
movq %r10, 32(%rsi)
dest
movq %rbp, 40(%rsi)
movq %r15, 40(%rsi)
dest
movq %r14, 48(%rsi)
dest
......@@ -203,7 +203,7 @@ ENTRY(csum_partial_copy_generic)
movq 3*8(%rsp), %r12
movq 4*8(%rsp), %r14
movq 5*8(%rsp), %r13
movq 6*8(%rsp), %rbp
movq 6*8(%rsp), %r15
addq $7*8, %rsp
ret
......
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