[PATCH] x86: don't destroy %rbp on kernel-mode faults
From: Vegard Nossum
Date: Mon May 19 2008 - 15:39:44 EST
>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.
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxx>
---
arch/x86/kernel/entry_64.S | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1edd9ac..ff53692 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -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
--
1.5.4.1
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