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ARM: backtrace-clang: avoid crash on bogus frame pointer
The Clang backtrace code dereferences the link register value pulled from the stack to decide whether the caller was a branch-and-link instruction, in order to subsequently decode the offset to find the start of the calling function. Unlike other loads in this routine, this one is not protected by a fixup, and may therefore cause a crash if the address in question is bogus. So let's fix this, by treating the fault as a failure to decode the 'bl' instruction. To avoid a label renum, reuse a fixup label that guards an instruction that cannot fault to begin with. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Marc Zyngier <maz@kernel.org> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
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@ -144,7 +144,7 @@ for_each_frame: tst frame, mask @ Check for address exceptions
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*/
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1003: ldr sv_lr, [sv_fp, #4] @ get saved lr from next frame
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ldr r0, [sv_lr, #-4] @ get call instruction
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1004: ldr r0, [sv_lr, #-4] @ get call instruction
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ldr r3, .Lopcode+4
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and r2, r3, r0 @ is this a bl call
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teq r2, r3
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@ -164,7 +164,7 @@ finished_setup:
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/*
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* Print the function (sv_pc) and where it was called from (sv_lr).
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*/
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1004: mov r0, sv_pc
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mov r0, sv_pc
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mov r1, sv_lr
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mov r2, frame
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@ -210,7 +210,7 @@ ENDPROC(c_backtrace)
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.long 1001b, 1006b
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.long 1002b, 1006b
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.long 1003b, 1006b
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.long 1004b, 1006b
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.long 1004b, finished_setup
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.long 1005b, 1006b
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.popsection
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