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 <mi...@neuling.org>
cc: sta...@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); \
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