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Message-Id: <4b03a961efda5ec9bfe46b7b9c9ad72d1efad343.1493909486.git.jpoimboe@redhat.com> Date: Thu, 4 May 2017 09:51:40 -0500 From: Josh Poimboeuf <jpoimboe@...hat.com> To: x86@...nel.org Cc: Andrey Konovalov <andreyknvl@...gle.com>, linux-kernel@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>, Neil Horman <nhorman@...driver.com>, "David S . Miller" <davem@...emloft.net>, linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Kostya Serebryany <kcc@...gle.com>, syzkaller <syzkaller@...glegroups.com>, Eric Dumazet <edumazet@...gle.com>, Cong Wang <xiyou.wangcong@...il.com> Subject: [PATCH] x86/asm: Don't use rbp as temp 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 be affected. Reported-by: Andrey Konovalov <andreyknvl@...gle.com> Tested-by: Andrey Konovalov <andreyknvl@...gle.com> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.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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