[Xen-devel] [PATCH 2/2] x86/emul: Bugfixes to SYSCALL emulation

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Introduce vendor_is() to allow emulation to have vendor-specific
behaviour.  Adjust the SYSCALL behaviour on Intel to raise #UD when
executed outside of 64bit mode.

in_longmode() has different return semantics from rc, so use a separate
integer for the purpose.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 54 ++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 165eebb..419c2da 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1327,6 +1327,45 @@ static bool vcpu_has(
 #define host_and_vcpu_must_have(feat) vcpu_must_have(feat)
 #endif
 
+#define X86_VENDOR_INTEL 0
+#define X86_VENDOR_AMD   2
+
+static bool vendor_is(
+    struct x86_emulate_ctxt *ctxt,
+    const struct x86_emulate_ops *ops,
+    int vendor)
+{
+    unsigned int eax = 0, ebx = 0, ecx = 0, edx = 0;
+    int rc = X86EMUL_OKAY;
+
+    fail_if(!ops->cpuid);
+    rc = ops->cpuid(&eax, &ebx, &ecx, &edx, ctxt);
+    if ( rc == X86EMUL_OKAY )
+    {
+        switch ( vendor )
+        {
+        case X86_VENDOR_INTEL:
+            return (ebx == 0x756e6547u && /* "GenuineIntel" */
+                    ecx == 0x6c65746eu &&
+                    edx == 0x49656e69u);
+
+        case X86_VENDOR_AMD:
+            return (ebx == 0x68747541u && /* "AuthenticAMD" */
+                    ecx == 0x444d4163u &&
+                    edx == 0x69746e65u);
+        default:
+            rc = ~X86EMUL_OKAY;
+            break;
+        }
+    }
+
+ done:
+    return rc == X86EMUL_OKAY;
+}
+
+#define vendor_is_intel() vendor_is(ctxt, ops, X86_VENDOR_INTEL)
+#define vendor_is_amd()   vendor_is(ctxt, ops, X86_VENDOR_AMD)
+
 static int
 in_longmode(
     struct x86_emulate_ctxt *ctxt,
@@ -4623,10 +4662,15 @@ x86_emulate(
         break;
     }
 
-    case X86EMUL_OPC(0x0f, 0x05): /* syscall */ {
+    case X86EMUL_OPC(0x0f, 0x05): /* syscall */
+    {
         uint64_t msr_content;
+#ifdef __x86_64__
+        int lm;
+#endif
 
-        generate_exception_if(!in_protmode(ctxt, ops), EXC_UD);
+        generate_exception_if(!in_protmode(ctxt, ops) ||
+                              (vendor_is_intel() && !mode_64bit()), EXC_UD);
 
         /* Inject #UD if syscall/sysret are disabled. */
         fail_if(ops->read_msr == NULL);
@@ -4645,10 +4689,10 @@ x86_emulate(
         sreg.attr.bytes = 0xc93; /* G+DB+P+S+Data */
 
 #ifdef __x86_64__
-        rc = in_longmode(ctxt, ops);
-        if ( rc < 0 )
+        lm = in_longmode(ctxt, ops);
+        if ( lm < 0 )
             goto cannot_emulate;
-        if ( rc )
+        if ( lm )
         {
             cs.attr.bytes = 0xa9b; /* L+DB+P+S+Code */
 
-- 
2.1.4


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