From b5bbf10ee6b65b70c10c139822bc2dc077cefa76 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Sun, 2 Nov 2014 11:54:46 +0200 Subject: [PATCH] KVM: x86: Emulation of MOV-sreg to memory uses incorrect size In x86, you can only MOV-sreg to memory with either 16-bits or 64-bits size. In contrast, KVM may write to 32-bits memory on MOV-sreg. This patch fixes KVM behavior, and sets the destination operand size to two, if the destination is memory. When destination is registers, and the operand size is 32-bits, the high 16-bits in modern CPUs is filled with zero. This is handled correctly. Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 736a49f..713295d 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -3207,6 +3207,8 @@ static int em_mov_rm_sreg(struct x86_emulate_ctxt *ctxt) return emulate_ud(ctxt); ctxt->dst.val = get_segment_selector(ctxt, ctxt->modrm_reg); + if (ctxt->dst.bytes == 4 && ctxt->dst.type == OP_MEM) + ctxt->dst.bytes = 2; return X86EMUL_CONTINUE; } -- 2.7.4