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

Nicholas Piggin npiggin at gmail.com
Fri Mar 23 16:53:38 AEDT 2018

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: f0f558b131 ("powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address")
Cc: Paul Mackerras <paulus at ozlabs.org>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
 arch/powerpc/kernel/exceptions-64s.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3ac87e53b3da..1ecfd8ffb098 100644
--- 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

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