On 02/11/2017 09:31, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> Pedro reported:
> During tests that we conducted on KVM, we noticed that executing a "PUSH %ES"
> instruction under KVM produces different results on both memory and the SP
> register depending on whether EPT support is enabled. With EPT the SP is
> reduced by 4 bytes (and the written value is 0-padded) but without EPT support
> it is only reduced by 2 bytes. The difference can be observed when the CS.DB
> field is 1 (32-bit) but not when it's 0 (16-bit).
>
> The internal segment descriptor cache exist even in real/vm8096 mode. The CS.D
> also should be respected instead of just default operand-size/66H prefix during
> instruction decoding. This patch fixes it by also adjusting operand-size according
> to CS.D.
>
> Reported-by: Pedro Fonseca <pfonseca@xxxxxxxxxxxxxxxxx>
> Tested-by: Pedro Fonseca <pfonseca@xxxxxxxxxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
> Cc: Pedro Fonseca <pfonseca@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> v2 -> v3:
> * cleanup the codes
> v1 -> v2:
> * respect cs.d for real/vm8096, other modes have already
> been considered in init_emulate_ctxt().
>
> arch/x86/kvm/emulate.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 8079d14..6ebc4cb 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5000,6 +5000,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
> bool op_prefix = false;
> bool has_seg_override = false;
> struct opcode opcode;
> + u16 dummy;
> + struct desc_struct desc;
>
> ctxt->memop.type = OP_NONE;
> ctxt->memopp = NULL;
> @@ -5020,6 +5022,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
> case X86EMUL_MODE_VM86:
> case X86EMUL_MODE_PROT16:
> def_op_bytes = def_ad_bytes = 2;
> + if (mode < X86EMUL_MODE_PROT16) {
> + ctxt->ops->get_segment(ctxt, &dummy, &desc, NULL, VCPU_SREG_CS);
> + if (desc.d)
> + def_op_bytes = 4;
def_ad_bytes must be changed to 4 as well. With that change, you should
probably separate X86EMUL_MODE_PROT16 altogether from the others.
Paolo
> + }
> break;
> case X86EMUL_MODE_PROT32:
> def_op_bytes = def_ad_bytes = 4;
>
