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Commit f0705804 authored by Wanpeng Li's avatar Wanpeng Li Committed by Greg Kroah-Hartman
Browse files

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




[ 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: default avatarPedro Fonseca <pfonseca@cs.washington.edu>
Tested-by: default avatarPedro 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: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 6ca9bcfe

arch/x86/kvm/emulate.c

+7 −0
Original line number Diff line number Diff line
@@ -4385,6 +4385,8 @@ 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;
@@ -4403,6 +4405,11 @@ 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;