4.9-stable review patch.  If anyone has any objections, please let me know.


From: Nicholas Piggin <npig...@gmail.com>

commit 52396500f97c53860164debc7d4f759077853423 upstream.

The SLB bad address handler's trap number fixup does not preserve the
low bit that indicates nonvolatile GPRs have not been saved. This
leads save_nvgprs to skip saving them, and subsequent functions and
return from interrupt will think they are saved.

This causes kernel branch-to-garbage debugging to not have correct
registers, can also cause userspace to have its registers clobbered
after a segfault.

Fixes: f0f558b131db ("powerpc/mm: Preserve CFAR value on SLB miss caused by 
access to bogus address")
Cc: sta...@vger.kernel.org # v4.9+
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 arch/powerpc/kernel/exceptions-64s.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -723,7 +723,7 @@ EXC_COMMON_BEGIN(bad_addr_slb)
        ld      r3, PACA_EXSLB+EX_DAR(r13)
        std     r3, _DAR(r1)
        beq     cr6, 2f
-       li      r10, 0x480              /* fix trap number for I-SLB miss */
+       li      r10, 0x481              /* fix trap number for I-SLB miss */
        std     r10, _TRAP(r1)
 2:     bl      save_nvgprs
        addi    r3, r1, STACK_FRAME_OVERHEAD

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