x86/emul: Fix the handling of unimplemented Grp7 instructions

Grp7 is abnormally complicated to decode, even by x86's standards, with
{s,l}msw being the problematic cases.

Previously, any value which fell through the first switch statement (looking
for instructions with entirely implicit operands) would be interpreted by the
second switch statement (handling instructions with memory operands).

Unimplemented instructions would then hit the #UD case for having a non-memory
operand, rather than taking the cannot_emulate path.

Consolidate the two switch statements into a single one, using ranges to cover
the instructions with memory operands.

Reported-by: Petre Pircalabu <ppircalabu@bitdefender.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <JBeulich@suse.com>
master commit: 4d3f0fde47
master date: 2017-09-05 12:58:47 +0100

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -4370,9 +4370,12 @@ x86_emulate(
         }
         break;
 
-    case X86EMUL_OPC(0x0f, 0x01): /* Grp7 */ {
+    case X86EMUL_OPC(0x0f, 0x01): /* Grp7 */
+    {
         unsigned long base, limit, cr0, cr0w;
 
+        seg = (modrm_reg & 1) ? x86_seg_idtr : x86_seg_gdtr;
+
         switch( modrm )
         {
 #ifdef __XEN__
@@ -4388,7 +4391,7 @@ x86_emulate(
                                   handle_xsetbv(_regs._ecx,
                                                 _regs._eax | (_regs.rdx << 32)),
                                   EXC_GP, 0);
-            goto no_writeback;
+            break;
         }
 #endif
 
@@ -4398,7 +4401,7 @@ x86_emulate(
             fail_if(!ops->vmfunc);
             if ( (rc = ops->vmfunc(ctxt)) != X86EMUL_OKAY )
                 goto done;
-            goto no_writeback;
+            break;
 
         case 0xd5: /* xend */
             generate_exception_if(vex.pfx, EXC_UD, -1);
@@ -4412,7 +4415,7 @@ x86_emulate(
                                   EXC_UD, -1);
             /* Neither HLE nor RTM can be active when we get here. */
             _regs.eflags |= EFLG_ZF;
-            goto no_writeback;
+            break;
 
         case 0xdf: /* invlpga */
             generate_exception_if(!in_protmode(ctxt, ops), EXC_UD, -1);
@@ -4421,7 +4424,7 @@ x86_emulate(
             if ( (rc = ops->invlpg(x86_seg_none, truncate_ea(_regs.eax),
                                    ctxt)) )
                 goto done;
-            goto no_writeback;
+            break;
 
         case 0xf9: /* rdtscp */
         {
@@ -4471,17 +4474,17 @@ x86_emulate(
                 base += sizeof(zero);
                 limit -= sizeof(zero);
             }
-            goto no_writeback;
-        }
+            break;
         }
 
-        seg = (modrm_reg & 1) ? x86_seg_idtr : x86_seg_gdtr;
+#define _GRP7(mod, reg) \
+            (((mod) << 6) | ((reg) << 3)) ... (((mod) << 6) | ((reg) << 3) | 7)
+#define GRP7_MEM(reg) _GRP7(0, reg): case _GRP7(1, reg): case _GRP7(2, reg)
+#define GRP7_ALL(reg) GRP7_MEM(reg): case _GRP7(3, reg)
 
-        switch ( modrm_reg & 7 )
-        {
-        case 0: /* sgdt */
-        case 1: /* sidt */
-            generate_exception_if(ea.type != OP_MEM, EXC_UD, -1);
+        case GRP7_MEM(0): /* sgdt */
+        case GRP7_MEM(1): /* sidt */
+            ASSERT(ea.type == OP_MEM);
             generate_exception_if(umip_active(ctxt, ops), EXC_GP, 0);
             fail_if(ops->read_segment == NULL);
             if ( (rc = ops->read_segment(seg, &sreg, ctxt)) )
@@ -4499,10 +4502,11 @@ x86_emulate(
                                   op_bytes, ctxt)) != X86EMUL_OKAY )
                 goto done;
             break;
-        case 2: /* lgdt */
-        case 3: /* lidt */
+
+        case GRP7_MEM(2): /* lgdt */
+        case GRP7_MEM(3): /* lidt */
+            ASSERT(ea.type == OP_MEM);
             generate_exception_if(!mode_ring0(), EXC_GP, 0);
-            generate_exception_if(ea.type != OP_MEM, EXC_UD, -1);
             fail_if(ops->write_segment == NULL);
             memset(&sreg, 0, sizeof(sreg));
             if ( (rc = read_ulong(ea.mem.seg, ea.mem.off+0,
@@ -4518,7 +4522,8 @@ x86_emulate(
             if ( (rc = ops->write_segment(seg, &sreg, ctxt)) )
                 goto done;
             break;
-        case 4: /* smsw */
+
+        case GRP7_ALL(4): /* smsw */
             generate_exception_if(umip_active(ctxt, ops), EXC_GP, 0);
             ea.bytes = (ea.type == OP_MEM) ? 2 : op_bytes;
             dst = ea;
@@ -4527,7 +4532,8 @@ x86_emulate(
                 goto done;
             d |= Mov; /* force writeback */
             break;
-        case 6: /* lmsw */
+
+        case GRP7_ALL(6): /* lmsw */
             fail_if(ops->read_cr == NULL);
             fail_if(ops->write_cr == NULL);
             generate_exception_if(!mode_ring0(), EXC_GP, 0);
@@ -4543,13 +4549,19 @@ x86_emulate(
             if ( (rc = ops->write_cr(0, cr0, ctxt)) )
                 goto done;
             break;
-        case 7: /* invlpg */
+
+        case GRP7_MEM(7): /* invlpg */
+            ASSERT(ea.type == OP_MEM);
             generate_exception_if(!mode_ring0(), EXC_GP, 0);
-            generate_exception_if(ea.type != OP_MEM, EXC_UD, -1);
             fail_if(ops->invlpg == NULL);
             if ( (rc = ops->invlpg(ea.mem.seg, ea.mem.off, ctxt)) )
                 goto done;
             break;
+
+#undef GRP7_ALL
+#undef GRP7_MEM
+#undef _GRP7
+
         default:
             goto cannot_emulate;
         }
@@ -5477,7 +5489,6 @@ x86_emulate(
         break;
     }
 
- no_writeback:
     /* Commit shadow register state. */
     _regs.eflags &= ~EFLG_RF;