Commit 90ff5d68 authored Dec 16, 2013 by Michael Neuling Committed by Benjamin Herrenschmidt Dec 30, 2013

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>

parent 803c2d2f

arch/powerpc/include/asm/exception-64s.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -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); \