x86emul: add XOP decoding

This way we can at least size (and e.g. skip) them if needed, and we
also won't raise the wrong fault due to not having read all relevant
bytes.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -279,6 +279,12 @@ static const opcode_desc_t twobyte_table[256] = {
     ModRM, ModRM, ModRM, ModRM, ModRM, ModRM, ModRM, ModRM
 };
 
+static const opcode_desc_t xop_table[] = {
+    DstReg|SrcImmByte|ModRM,
+    DstReg|SrcMem|ModRM,
+    DstReg|SrcImm|ModRM,
+};
+
 #define REX_PREFIX 0x40
 #define REX_B 0x01
 #define REX_X 0x02
@@ -1591,6 +1597,13 @@ struct x86_emulate_state {
         ext_0f   = vex_0f,
         ext_0f38 = vex_0f38,
         ext_0f3a = vex_0f3a,
+        /*
+         * For XOP use values such that the respective instruction field
+         * can be used without adjustment.
+         */
+        ext_8f08 = 8,
+        ext_8f09,
+        ext_8f0a,
     } ext;
     uint8_t opcode;
     uint8_t modrm, modrm_mod, modrm_reg, modrm_rm;
@@ -1813,7 +1826,7 @@ x86_decode(
         modrm = insn_fetch_type(uint8_t);
         modrm_mod = (modrm & 0xc0) >> 6;
 
-        if ( !ext && ((b & ~1) == 0xc4) )
+        if ( !ext && ((b & ~1) == 0xc4 || (b == 0x8f && (modrm & 0x18))) )
             switch ( def_ad_bytes )
             {
             default:
@@ -1827,11 +1840,11 @@ x86_decode(
                     break;
                 /* fall through */
             case 8:
-                /* VEX */
+                /* VEX / XOP */
                 generate_exception_if(rex_prefix || vex.pfx, EXC_UD, -1);
 
                 vex.raw[0] = modrm;
-                if ( b & 1 )
+                if ( b == 0xc5 )
                 {
                     vex.raw[1] = modrm;
                     vex.opcx = vex_0f;
@@ -1859,18 +1872,30 @@ x86_decode(
                     rex_prefix |= REX_R;
 
                 b = insn_fetch_type(uint8_t);
-                switch ( ext = vex.opcx )
+                ext = vex.opcx;
+                if ( b != 0x8f )
+                {
+                    switch ( ext )
+                    {
+                    case vex_0f:
+                        d = twobyte_table[b];
+                        break;
+                    case vex_0f38:
+                        d = twobyte_table[0x38];
+                        break;
+                    case vex_0f3a:
+                        d = twobyte_table[0x3a];
+                        break;
+                    default:
+                        rc = X86EMUL_UNHANDLEABLE;
+                        goto done;
+                    }
+                }
+                else if ( ext < ext_8f08 +
+                                sizeof(xop_table) / sizeof(*xop_table) )
+                    d = xop_table[ext - ext_8f08];
+                else
                 {
-                case vex_0f:
-                    d = twobyte_table[b];
-                    break;
-                case vex_0f38:
-                    d = twobyte_table[0x38];
-                    break;
-                case vex_0f3a:
-                    d = twobyte_table[0x3a];
-                    break;
-                default:
                     rc = X86EMUL_UNHANDLEABLE;
                     goto done;
                 }
@@ -1932,6 +1957,9 @@ x86_decode(
 
         case ext_0f:
         case ext_0f3a:
+        case ext_8f08:
+        case ext_8f09:
+        case ext_8f0a:
             break;
 
         case ext_0f38:
@@ -2121,6 +2149,9 @@ x86_decode(
 
     case ext_0f38:
     case ext_0f3a:
+    case ext_8f08:
+    case ext_8f09:
+    case ext_8f0a:
         break;
 
     default:
@@ -2337,6 +2368,9 @@ x86_emulate(
     default:
         ASSERT_UNREACHABLE();
     case ext_0f3a:
+    case ext_8f08:
+    case ext_8f09:
+    case ext_8f0a:
         goto cannot_emulate;
     }