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x86: don't destroy %rbp on kernel-mode faults

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From the code:

    "B stepping K8s sometimes report an truncated RIP for IRET exceptions
    returning to compat mode. Check for these here too."

The code then proceeds to truncate the upper 32 bits of %rbp. This means
that when do_page_fault() is finally called, its prologue,

    do_page_fault:
        push %rbp
        movl %rsp, %rbp

will put the truncated base pointer on the stack. This means that the
stack tracer will not be able to follow the base-pointer changes and
will see all subsequent stack frames as unreliable.

This patch changes the code to use a different register (%rcx) for the
checking and leaves %rbp untouched.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Vegard Nossum 2008-06-27 17:22:17 +02:00 committed by Ingo Molnar
parent 543cf4cb3f
commit 9d8ad5d6c7
1 changed files with 4 additions and 4 deletions
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8
arch/x86/kernel/entry_64.S
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@ -926,11 +926,11 @@ error_kernelspace:
iret run with kernel gs again, so don't set the user space flag.
B stepping K8s sometimes report an truncated RIP for IRET
exceptions returning to compat mode. Check for these here too. */
leaq irq_return(%rip),%rbp
cmpq %rbp,RIP(%rsp)
leaq irq_return(%rip),%rcx
cmpq %rcx,RIP(%rsp)
je error_swapgs
movl %ebp,%ebp /* zero extend */
cmpq %rbp,RIP(%rsp)
movl %ecx,%ecx /* zero extend */
cmpq %rcx,RIP(%rsp)
je error_swapgs
cmpq $gs_change,RIP(%rsp)
je error_swapgs