[PATCH] KVM: x86 emulator: reject SYSENTER in compatibility mode on AMD guests

[Avi Kivity <avi@redhat.com>]

If the guest thinks it's an AMD, it will not have prepared the SYSENTER MSRs,
and if the guest executes SYSENTER in compatibility mode, it will fails.

Detect this condition and #UD instead, like the spec says.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/kvm/emulate.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6eaedac..367bd06 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1892,6 +1892,16 @@ static int em_lseg(struct x86_emulate_ctxt *ctxt)
 	ss->p = 1;
 }
 
+static bool vendor_intel(struct x86_emulate_ctxt *ctxt)
+{
+	u32 eax, ebx, ecx, edx;
+
+	return ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)
+		&& ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
+		&& ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx
+		&& edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
+}
+
 static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
 {
 	struct x86_emulate_ops *ops = ctxt->ops;
@@ -2008,6 +2018,14 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
 	if (ctxt->mode == X86EMUL_MODE_REAL)
 		return emulate_gp(ctxt, 0);
 
+	/*
+	 * Not recognized on AMD in compat mode (but is recognized in legacy
+	 * mode).
+	 */
+	if ((ctxt->mode == X86EMUL_MODE_PROT32) && (efer & EFER_LMA)
+	    && !vendor_intel(ctxt))
+		return emulate_ud(ctxt);
+
 	/* XXX sysenter/sysexit have not been tested in 64bit mode.
 	* Therefore, we inject an #UD.
 	*/
-- 
1.7.9