powerpc/64s: Fix i-side SLB miss bad address handler saving nonvolatile GPRs

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: stable@vger.kernel.org # v4.9+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3ac87e5..1ecfd8f 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -706,7 +706,7 @@ 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