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

PATCH Applied Nicholas Piggin 2 participants 2 messages Mar 23, 2018 – Mar 25, 2018 PowerPC

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Nicholas Piggin

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PATCH 1/1 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 f0f558b131 ("powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address")
Cc Paul Mackerras <[email protected]>
Signed-off-by Nicholas Piggin <[email protected]>
---
 arch/powerpc/kernel/exceptions-64s.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
arch/powerpc/kernel/exceptions-64s.S +1 -1
index 3ac87e53b3da..1ecfd8ffb098 100644
@@ -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
Signature · 1 line
2.16.1
Applied
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Quoted 5 lines · Nicholas Piggin

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.

Quoted 7 lines

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 <[email protected]>
Signed-off-by Nicholas Piggin <[email protected]>

I added:
Cc: [email protected] # v4.9+

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/52396500f97c53860164debc7d4f75

cheers