| From: Michael Neuling <mikey@neuling.org> |
| Date: Mon, 16 Dec 2013 15:12:43 +1100 |
| Subject: powerpc: Fix bad stack check in exception entry |
| |
| commit 90ff5d688e61f49f23545ffab6228bd7e87e6dc7 upstream. |
| |
| 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> |
| Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| arch/powerpc/include/asm/exception-64s.h | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/arch/powerpc/include/asm/exception-64s.h |
| +++ b/arch/powerpc/include/asm/exception-64s.h |
| @@ -163,7 +163,7 @@ 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); \ |
