Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [PATCH 2/6] KVM: x86: Wrong emulation on 'xadd X, X' | Date | Sun, 15 Jun 2014 16:12:58 +0300 |
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The emulator does not emulate the xadd instruction correctly if the two operands are the same. In this (unlikely) situation the result should be the sum of X and X (2X) when it is currently X. The solution is to first perform writeback to the source, before writing to the destination. The only instruction which should be affected is xadd, as the other instructions that perform writeback to the source use the extended accumlator (e.g., RAX:RDX).
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il> --- arch/x86/kvm/emulate.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index f0b0a10..3c8d867 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4711,17 +4711,17 @@ special_insn: goto done; writeback: - if (!(ctxt->d & NoWrite)) { - rc = writeback(ctxt, &ctxt->dst); - if (rc != X86EMUL_CONTINUE) - goto done; - } if (ctxt->d & SrcWrite) { BUG_ON(ctxt->src.type == OP_MEM || ctxt->src.type == OP_MEM_STR); rc = writeback(ctxt, &ctxt->src); if (rc != X86EMUL_CONTINUE) goto done; } + if (!(ctxt->d & NoWrite)) { + rc = writeback(ctxt, &ctxt->dst); + if (rc != X86EMUL_CONTINUE) + goto done; + } /* * restore dst type in case the decoding will be reused -- 1.9.1
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