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KVM: X86: Fix operand/address-size during instruction decoding

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[ Upstream commit 3853be2603191829b442b64dac6ae8ba0c027bf9 ]

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/address-size/66H
prefix/67H prefix during instruction decoding. This patch fixes it by also
adjusting operand/address-size according to CS.D.

Reported-by: Pedro Fonseca <pfonseca@cs.washington.edu>
Tested-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>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Wanpeng Li 2017-11-05 16:54:47 -08:00 committed by Greg Kroah-Hartman
parent df54fc5c28
commit 4f5500a634
1 changed files with 7 additions and 0 deletions
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7
arch/x86/kvm/emulate.c
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@ -5009,6 +5009,8 @@ 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;
@ -5027,6 +5029,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
switch (mode) {
case X86EMUL_MODE_REAL:
case X86EMUL_MODE_VM86:
def_op_bytes = def_ad_bytes = 2;
ctxt->ops->get_segment(ctxt, &dummy, &desc, NULL, VCPU_SREG_CS);
if (desc.d)
def_op_bytes = def_ad_bytes = 4;
break;
case X86EMUL_MODE_PROT16:
def_op_bytes = def_ad_bytes = 2;
break;