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powerpc: Fix bad stack check in exception entry
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 Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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@ -284,7 +284,7 @@ do_kvm_##n: \
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subi r1,r1,INT_FRAME_SIZE; /* alloc frame on kernel stack */ \
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beq- 1f; \
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ld r1,PACAKSAVE(r13); /* kernel stack to use */ \
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1: cmpdi cr1,r1,0; /* check if r1 is in userspace */ \
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1: cmpdi cr1,r1,-INT_FRAME_SIZE; /* check if r1 is in userspace */ \
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blt+ cr1,3f; /* abort if it is */ \
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li r1,(n); /* will be reloaded later */ \
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sth r1,PACA_TRAP_SAVE(r13); \
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