2 files changed, 64 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index c8b28689eeeb..7b9cfc4878af 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -301,6 +301,19 @@ struct x86_emulate_ctxt {
 #define X86EMUL_MODE_PROT     (X86EMUL_MODE_PROT16|X86EMUL_MODE_PROT32| \
                                X86EMUL_MODE_PROT64)
 
+/* CPUID vendors */
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx 0x68747541
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx 0x444d4163
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_edx 0x69746e65
+
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx 0x69444d41
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx 0x21726574
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_edx 0x74656273
+
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_ebx 0x756e6547
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_ecx 0x6c65746e
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_edx 0x49656e69
+
 enum x86_intercept_stage {
         X86_ICTP_NONE = 0,   /* Allow zero-init to not match anything */
         X86_ICPT_PRE_EXCEPT,
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 05a562b85025..0982507b962a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1891,6 +1891,51 @@ setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
         ss->p = 1;
 }
 
+static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
+{
+        struct x86_emulate_ops *ops = ctxt->ops;
+        u32 eax, ebx, ecx, edx;
+
+        /*
+         * syscall should always be enabled in longmode - so only become
+         * vendor specific (cpuid) if other modes are active...
+         */
+        if (ctxt->mode == X86EMUL_MODE_PROT64)
+                return true;
+
+        eax = 0x00000000;
+        ecx = 0x00000000;
+        if (ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)) {
+                /*
+                 * Intel ("GenuineIntel")
+                 * remark: Intel CPUs only support "syscall" in 64bit
+                 * longmode. Also an 64bit guest with a
+                 * 32bit compat-app running will #UD !! While this
+                 * behaviour can be fixed (by emulating) into AMD
+                 * response - CPUs of AMD can't behave like Intel.
+                 */
+                if (ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
+                    ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
+                    edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx)
+                        return false;
+
+                /* AMD ("AuthenticAMD") */
+                if (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
+                    ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
+                    edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
+                        return true;
+
+                /* AMD ("AMDisbetter!") */
+                if (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
+                    ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
+                    edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx)
+                        return true;
+        }
+
+        /* default: (not Intel, not AMD), apply Intel's stricter rules... */
+        return false;
+}
+
 static int em_syscall(struct x86_emulate_ctxt *ctxt)
 {
         struct x86_emulate_ops *ops = ctxt->ops;
@@ -1904,9 +1949,15 @@ static int em_syscall(struct x86_emulate_ctxt *ctxt)
             ctxt->mode == X86EMUL_MODE_VM86)
                 return emulate_ud(ctxt);
 
+        if (!(em_syscall_is_enabled(ctxt)))
+                return emulate_ud(ctxt);
+
         ops->get_msr(ctxt, MSR_EFER, &efer);
         setup_syscalls_segments(ctxt, &cs, &ss);
 
+        if (!(efer & EFER_SCE))
+                return emulate_ud(ctxt);
+
         ops->get_msr(ctxt, MSR_STAR, &msr_data);
         msr_data >>= 32;
         cs_sel = (u16)(msr_data & 0xfffc);