| Message ID | 15350.1387167163@ale.ozlabs.ibm.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
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
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); \
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