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Groups > linux.kernel > #1635819 > unrolled thread
| Started by | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| First post | 2017-05-04 17:00 +0200 |
| Last post | 2017-05-05 10:30 +0200 |
| Articles | 4 — 3 participants |
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[PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-04 17:00 +0200
RE: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() David Laight <David.Laight@ACULAB.COM> - 2017-05-04 18:10 +0200
Re: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-04 18:20 +0200
[tip:x86/urgent] x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic() tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2017-05-05 10:30 +0200
| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-05-04 17:00 +0200 |
| Subject | [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() |
| Message-ID | <tDqoy-4PF-15@gated-at.bofh.it> |
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
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| From | David Laight <David.Laight@ACULAB.COM> |
|---|---|
| Date | 2017-05-04 18:10 +0200 |
| Subject | RE: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() |
| Message-ID | <tDruh-5So-5@gated-at.bofh.it> |
| In reply to | #1635819 |
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
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| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-05-04 18:20 +0200 |
| Subject | Re: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic() |
| Message-ID | <tDrDY-5WC-9@gated-at.bofh.it> |
| In reply to | #1635867 |
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
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| From | tip-bot for Josh Poimboeuf <tipbot@zytor.com> |
|---|---|
| Date | 2017-05-05 10:30 +0200 |
| Subject | [tip:x86/urgent] x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic() |
| Message-ID | <tDGMF-7Ep-7@gated-at.bofh.it> |
| In reply to | #1635819 |
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
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