From: Wanpeng Li wanpeng.li@hotmail.com
[ 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@microsoft.com --- 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 c8f8dd8ca0a1..6f5a3b076341 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4990,6 +4990,8 @@ 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; @@ -5008,6 +5010,11 @@ 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;