* [PATCH] powerpc: Fix bad stack check in exception entry
@ 2013-12-16 4:12 Michael Neuling
2013-12-18 1:55 ` Michael Ellerman
0 siblings, 1 reply; 2+ messages in thread
From: Michael Neuling @ 2013-12-16 4:12 UTC (permalink / raw)
To: benh; +Cc: Linux PPC dev, Paul Mackerras, anton
In EXCEPTION_PROLOG_COMMON() we check to see if the stack pointer (r1)
is valid when coming from the kernel. If it's not valid, we die but
with a nice oops message.
Currently we allocate a stack frame (subtract INT_FRAME_SIZE) before we
check to see if the stack pointer is negative. Unfortunately, this
won't detect a bad stack where r1 is less than INT_FRAME_SIZE.
This patch fixes the check to compare the modified r1 with
-INT_FRAME_SIZE. With this, bad kernel stack pointers (including NULL
pointers) are correctly detected again.
Kudos to Paulus for finding this.
Signed-off-by: Michael Neuling <mikey@neuling.org>
cc: stable@vger.kernel.org
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 894662a..243ce69 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -284,7 +284,7 @@ do_kvm_##n: \
subi r1,r1,INT_FRAME_SIZE; /* alloc frame on kernel stack */ \
beq- 1f; \
ld r1,PACAKSAVE(r13); /* kernel stack to use */ \
-1: cmpdi cr1,r1,0; /* check if r1 is in userspace */ \
+1: cmpdi cr1,r1,-INT_FRAME_SIZE; /* check if r1 is in userspace */ \
blt+ cr1,3f; /* abort if it is */ \
li r1,(n); /* will be reloaded later */ \
sth r1,PACA_TRAP_SAVE(r13); \
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] powerpc: Fix bad stack check in exception entry
2013-12-16 4:12 [PATCH] powerpc: Fix bad stack check in exception entry Michael Neuling
@ 2013-12-18 1:55 ` Michael Ellerman
0 siblings, 0 replies; 2+ messages in thread
From: Michael Ellerman @ 2013-12-18 1:55 UTC (permalink / raw)
To: Michael Neuling; +Cc: Paul Mackerras, anton, Linux PPC dev
On Mon, 2013-12-16 at 15:12 +1100, Michael Neuling wrote:
> In EXCEPTION_PROLOG_COMMON() we check to see if the stack pointer (r1)
> is valid when coming from the kernel. If it's not valid, we die but
> with a nice oops message.
>
> Currently we allocate a stack frame (subtract INT_FRAME_SIZE) before we
> check to see if the stack pointer is negative. Unfortunately, this
> won't detect a bad stack where r1 is less than INT_FRAME_SIZE.
The key detail being that we *expect* a negative value, because kernel
addresses (0xc000000000000000) are negative.
cheers
^ permalink raw reply [flat|nested] 2+ messages in thread
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