On 02/11/2014 10:54, Nadav Amit wrote:
> In x86, you cannot MOV-sreg to memory is either 16-bits or 64-bits. When
> destination is registers, and the operand size is 32-bits, the high 16-bits in
> modern CPUs is filled with zero.
>
> In contrast, KVM may write to memory 32-bits on MOV-sreg. This patch fixes KVM
> behavior, and sets the destination operand size to two, if the destination is
> memory.
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 <namit@xxxxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Paolo
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
> ---
> 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 273c37e..f456783 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3187,6 +3187,8 @@ 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;
> }
>
>
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