From 3853be2603191829b442b64dac6ae8ba0c027bf9 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Sun, 5 Nov 2017 16:54:47 -0800 Subject: [PATCH] KVM: X86: Fix operand/address-size during instruction decoding MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Tested-by: Pedro Fonseca Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Nadav Amit Cc: Pedro Fonseca Signed-off-by: Wanpeng Li Reviewed-by: Paolo Bonzini Signed-off-by: Radim Krčmář --- 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 8079d141792a..b4a87debbb4b 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; @@ -5018,6 +5020,11 @@ 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; -- 2.30.2