Re: [PATCH] powerpc/lib/sstep.c - Fix emulation fall-through

[Andrew Donnellan]

On 16/02/16 10:28, Oliver O'Halloran wrote:

There is a switch fallthough in instr_analyze() which can cause
an invalid instruction to be emulated as a different, valid,
instruction. The rld* (opcode 30) case extracts a sub-opcode from
bits 3:1 of the instruction word. However, the only valid values
of this field a 001 and 000. These cases are correctly handled,
but the others are not which causes execution to fall through
into case 31.

Breaking out of the switch causes the instruction to be marked as
unknown and allows the caller to deal with the invalid instruction
in a manner consistent with other invalid instructions.

Signed-off-by: Oliver O'Halloran 


The title should probably be "powerpc/sstep: fix switch fallthrough in 
instruction emulation" to be consistent with our usual patch titling 
practice. Please respin.


Apart from that, I'm reasonably convinced this is an appropriate fix:

Reviewed-by: Andrew Donnellan 

--
Andrew Donnellan  Software Engineer, OzLabs
andrew.donnel...@au1.ibm.com  Australia Development Lab, Canberra
+61 2 6201 8874 (work)IBM Australia Limited

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[PATCH] powerpc/lib/sstep.c - Fix emulation fall-through

[Oliver O'Halloran]

There is a switch fallthough in instr_analyze() which can cause
an invalid instruction to be emulated as a different, valid,
instruction. The rld* (opcode 30) case extracts a sub-opcode from
bits 3:1 of the instruction word. However, the only valid values
of this field a 001 and 000. These cases are correctly handled,
but the others are not which causes execution to fall through
into case 31.

Breaking out of the switch causes the instruction to be marked as
unknown and allows the caller to deal with the invalid instruction
in a manner consistent with other invalid instructions.

Signed-off-by: Oliver O'Halloran 
---
 arch/powerpc/lib/sstep.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index dc885b3..e25f73c 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -925,6 +925,7 @@ int __kprobes analyse_instr(struct instruction_op *op, 
struct pt_regs *regs,
}
}
 #endif
+   break; /* illegal instruction */
 
case 31:
switch ((instr >> 1) & 0x3ff) {
-- 
2.5.0

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