Messages in this thread | | | Subject | Re: [PATCH v2 1/2] KVM: X86: Fix operand size during instruction decoding | From | Pedro Fonseca <> | Date | Tue, 31 Oct 2017 19:35:24 -0700 |
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This patch fixes the problem and passes my tests on the CS.DB field, this includes the "push es" and the "high 16-bits of ESP" test cases.
Tested-by: Pedro Fonseca <pfonseca@cs.washington.edu>
On 10/27/17 1:36 AM, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > 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@cs.washington.edu> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Nadav Amit <nadav.amit@gmail.com> > Cc: Pedro Fonseca <pfonseca@cs.washington.edu> > Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> > --- > 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_REAL || mode == X86EMUL_MODE_VM86) { > + ctxt->ops->get_segment(ctxt, &dummy, &desc, NULL, VCPU_SREG_CS); > + if (desc.d) > + def_op_bytes = 4; > + } > break; > case X86EMUL_MODE_PROT32: > def_op_bytes = def_ad_bytes = 4;
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