* [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic()
@ 2017-05-04 14:51 Josh Poimboeuf
2017-05-04 15:56 ` David Laight
2017-05-05 8:10 ` [tip:x86/urgent] x86/asm: Don't use RBP as a temporary " tip-bot for Josh Poimboeuf
0 siblings, 2 replies; 4+ messages in thread
From: Josh Poimboeuf @ 2017-05-04 14:51 UTC (permalink / raw)
To: x86
Cc: Andrey Konovalov, linux-kernel, Vlad Yasevich, Neil Horman,
David S . Miller, linux-sctp, netdev, Marcelo Ricardo Leitner,
Dmitry Vyukov, Kostya Serebryany, syzkaller, Eric Dumazet,
Cong Wang
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 be affected.
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/lib/csum-copy_64.S | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/lib/csum-copy_64.S b/arch/x86/lib/csum-copy_64.S
index 7e48807..45a53df 100644
--- a/arch/x86/lib/csum-copy_64.S
+++ b/arch/x86/lib/csum-copy_64.S
@@ -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
--
2.7.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* RE: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic()
2017-05-04 14:51 [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() Josh Poimboeuf
@ 2017-05-04 15:56 ` David Laight
2017-05-04 16:11 ` Josh Poimboeuf
2017-05-05 8:10 ` [tip:x86/urgent] x86/asm: Don't use RBP as a temporary " tip-bot for Josh Poimboeuf
1 sibling, 1 reply; 4+ messages in thread
From: David Laight @ 2017-05-04 15:56 UTC (permalink / raw)
To: 'Josh Poimboeuf', x86
Cc: Andrey Konovalov, linux-kernel, Vlad Yasevich, Neil Horman,
David S . Miller, linux-sctp, netdev, Marcelo Ricardo Leitner,
Dmitry Vyukov, Kostya Serebryany, syzkaller, Eric Dumazet,
Cong Wang
From: Josh Poimboeuf
> Sent: 04 May 2017 15:52
> 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.
Does gcc guarantee not to use bp as a scratch register in leaf functions?
David
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic()
2017-05-04 15:56 ` David Laight
@ 2017-05-04 16:11 ` Josh Poimboeuf
0 siblings, 0 replies; 4+ messages in thread
From: Josh Poimboeuf @ 2017-05-04 16:11 UTC (permalink / raw)
To: David Laight
Cc: x86, Andrey Konovalov, linux-kernel, Vlad Yasevich, Neil Horman,
David S . Miller, linux-sctp, netdev, Marcelo Ricardo Leitner,
Dmitry Vyukov, Kostya Serebryany, syzkaller, Eric Dumazet,
Cong Wang
On Thu, May 04, 2017 at 03:56:49PM +0000, David Laight wrote:
> From: Josh Poimboeuf
> > Sent: 04 May 2017 15:52
> > 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.
>
> Does gcc guarantee not to use bp as a scratch register in leaf functions?
At least in practice, gcc doesn't touch rbp in leaf functions. (I don't
know about guarantees.)
--
Josh
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip:x86/urgent] x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic()
2017-05-04 14:51 [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() Josh Poimboeuf
2017-05-04 15:56 ` David Laight
@ 2017-05-05 8:10 ` tip-bot for Josh Poimboeuf
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot for Josh Poimboeuf @ 2017-05-05 8:10 UTC (permalink / raw)
To: linux-tip-commits
Cc: linux-kernel, jpoimboe, nhorman, syzkaller, netdev, kcc,
marcelo.leitner, edumazet, torvalds, andreyknvl, mingo,
xiyou.wangcong, peterz, davem, dvyukov, tglx, vyasevich, hpa
Commit-ID: 42fc6c6cb1662ba2fa727dd01c9473c63be4e3b6
Gitweb: http://git.kernel.org/tip/42fc6c6cb1662ba2fa727dd01c9473c63be4e3b6
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Thu, 4 May 2017 09:51:40 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 5 May 2017 07:59:24 +0200
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 | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/lib/csum-copy_64.S b/arch/x86/lib/csum-copy_64.S
index 7e48807..45a53df 100644
--- a/arch/x86/lib/csum-copy_64.S
+++ b/arch/x86/lib/csum-copy_64.S
@@ -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
^ permalink raw reply related [flat|nested] 4+ messages in thread
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2017-05-04 14:51 [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() Josh Poimboeuf
2017-05-04 15:56 ` David Laight
2017-05-04 16:11 ` Josh Poimboeuf
2017-05-05 8:10 ` [tip:x86/urgent] x86/asm: Don't use RBP as a temporary " tip-bot for Josh Poimboeuf
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