x86emul: fetch all insn bytes during the decode phase

This way we can offer to callers the service of just sizing
instructions, and we also can better guarantee not to 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>

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 88f5d9d7938eacc8231dd1b5dc55b6fcb161a108..26c0502aaa3b3f7683dda9de0db0b92add1e65d5 100644 (file)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -129,8 +129,8 @@ static const opcode_desc_t opcode_table[256] = {
     ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
     ImplicitOps|Mov, ImplicitOps|Mov, ImplicitOps, ImplicitOps,
     /* 0xA0 - 0xA7 */
-    ByteOp|DstEax|SrcImplicit|Mov, DstEax|SrcImplicit|Mov,
-    ByteOp|ImplicitOps|Mov, ImplicitOps|Mov,
+    ByteOp|DstEax|SrcMem|Mov, DstEax|SrcMem|Mov,
+    ByteOp|DstMem|SrcEax|Mov, DstMem|SrcEax|Mov,
     ByteOp|ImplicitOps|Mov, ImplicitOps|Mov,
     ByteOp|ImplicitOps, ImplicitOps,
     /* 0xA8 - 0xAF */
@@ -1612,6 +1612,45 @@ struct x86_emulate_state {
 #define ea (state->ea)
 #define _regs (state->regs)
 
+static int
+x86_decode_onebyte(
+    struct x86_emulate_state *state,
+    struct x86_emulate_ctxt *ctxt,
+    const struct x86_emulate_ops *ops)
+{
+    int rc = X86EMUL_OKAY;
+
+    switch ( state->opcode )
+    {
+    case 0x9a: /* call (far, absolute) */
+    case 0xea: /* jmp (far, absolute) */
+        generate_exception_if(mode_64bit(), EXC_UD, -1);
+
+        imm1 = insn_fetch_bytes(op_bytes);
+        imm2 = insn_fetch_type(uint16_t);
+        break;
+
+    case 0xa0: case 0xa1: /* mov mem.offs,{%al,%ax,%eax,%rax} */
+    case 0xa2: case 0xa3: /* mov {%al,%ax,%eax,%rax},mem.offs */
+        /* Source EA is not encoded via ModRM. */
+        ea.mem.off = insn_fetch_bytes(ad_bytes);
+        break;
+
+    case 0xb8 ... 0xbf: /* mov imm{16,32,64},r{16,32,64} */
+        if ( op_bytes == 8 ) /* Fetch more bytes to obtain imm64. */
+            imm1 = ((uint32_t)imm1 |
+                    ((uint64_t)insn_fetch_type(uint32_t) << 32));
+        break;
+
+    case 0xc8: /* enter imm16,imm8 */
+        imm2 = insn_fetch_type(uint8_t);
+        break;
+    }
+
+ done:
+    return rc;
+}
+
 static int
 x86_decode(
     struct x86_emulate_state *state,
@@ -2005,10 +2044,29 @@ x86_decode(
     state->opcode = b;
     state->desc = d;
 
+    switch ( ext )
+    {
+    case ext_none:
+        rc = x86_decode_onebyte(state, ctxt, ops);
+        break;
+
+    case ext_0f:
+    case ext_0f38:
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+        return X86EMUL_UNHANDLEABLE;
+    }
+
  done:
     return rc;
 }
 
+/* No insn fetching past this point. */
+#undef insn_fetch_bytes
+#undef insn_fetch_type
+
 int
 x86_emulate(
     struct x86_emulate_ctxt *ctxt,
@@ -2571,6 +2629,8 @@ x86_emulate(
     case 0xc6 ... 0xc7: /* mov (sole member of Grp11) */
         generate_exception_if((modrm_reg & 7) != 0, EXC_UD, -1);
     case 0x88 ... 0x8b: /* mov */
+    case 0xa0 ... 0xa1: /* mov mem.offs,{%al,%ax,%eax,%rax} */
+    case 0xa2 ... 0xa3: /* mov {%al,%ax,%eax,%rax},mem.offs */
         dst.val = src.val;
         break;
 
@@ -2655,18 +2715,13 @@ x86_emulate(
 
     case 0x9a: /* call (far, absolute) */ {
         struct segment_register reg;
-        uint16_t sel;
-        uint32_t eip;
 
-        generate_exception_if(mode_64bit(), EXC_UD, -1);
+        ASSERT(!mode_64bit());
         fail_if(ops->read_segment == NULL);
 
-        eip = insn_fetch_bytes(op_bytes);
-        sel = insn_fetch_type(uint16_t);
-
         if ( (rc = ops->read_segment(x86_seg_cs, &reg, ctxt)) ||
-             (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
-             (validate_far_branch(&cs, eip),
+             (rc = load_seg(x86_seg_cs, imm2, 0, &cs, ctxt, ops)) ||
+             (validate_far_branch(&cs, imm1),
               rc = ops->write(x86_seg_ss, sp_pre_dec(op_bytes),
                               &reg.sel, op_bytes, ctxt)) ||
              (rc = ops->write(x86_seg_ss, sp_pre_dec(op_bytes),
@@ -2674,7 +2729,7 @@ x86_emulate(
              (rc = ops->write_segment(x86_seg_cs, &cs, ctxt)) )
             goto done;
 
-        _regs.eip = eip;
+        _regs.eip = imm1;
         break;
     }
 
@@ -2716,23 +2771,6 @@ x86_emulate(
         ((uint8_t *)&_regs.eax)[1] = (_regs.eflags & 0xd7) | 0x02;
         break;
 
-    case 0xa0 ... 0xa1: /* mov mem.offs,{%al,%ax,%eax,%rax} */
-        /* Source EA is not encoded via ModRM. */
-        dst.bytes = (d & ByteOp) ? 1 : op_bytes;
-        if ( (rc = read_ulong(ea.mem.seg, insn_fetch_bytes(ad_bytes),
-                              &dst.val, dst.bytes, ctxt, ops)) != 0 )
-            goto done;
-        break;
-
-    case 0xa2 ... 0xa3: /* mov {%al,%ax,%eax,%rax},mem.offs */
-        /* Destination EA is not encoded via ModRM. */
-        dst.type  = OP_MEM;
-        dst.mem.seg = ea.mem.seg;
-        dst.mem.off = insn_fetch_bytes(ad_bytes);
-        dst.bytes = (d & ByteOp) ? 1 : op_bytes;
-        dst.val   = (unsigned long)_regs.eax;
-        break;
-
     case 0xa4 ... 0xa5: /* movs */ {
         unsigned long nr_reps = get_rep_prefix();
         dst.bytes = (d & ByteOp) ? 1 : op_bytes;
@@ -2850,9 +2888,6 @@ x86_emulate(
         break;
 
     case 0xb8 ... 0xbf: /* mov imm{16,32,64},r{16,32,64} */
-        if ( dst.bytes == 8 ) /* Fetch more bytes to obtain imm64 */
-            src.val = ((uint32_t)src.val |
-                       ((uint64_t)insn_fetch_type(uint32_t) << 32));
         dst.reg = decode_register(
             (b & 7) | ((rex_prefix & 1) << 3), &_regs, 0);
         dst.val = src.val;
@@ -2916,7 +2951,7 @@ x86_emulate(
         goto les;
 
     case 0xc8: /* enter imm16,imm8 */ {
-        uint8_t depth = insn_fetch_type(uint8_t) & 31;
+        uint8_t depth = imm2 & 31;
         int i;
 
         dst.type = OP_REG;
@@ -3629,17 +3664,12 @@ x86_emulate(
         jmp_rel((int32_t)src.val);
         break;
 
-    case 0xea: /* jmp (far, absolute) */ {
-        uint16_t sel;
-        uint32_t eip;
-        generate_exception_if(mode_64bit(), EXC_UD, -1);
-        eip = insn_fetch_bytes(op_bytes);
-        sel = insn_fetch_type(uint16_t);
-        if ( (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
-             (rc = commit_far_branch(&cs, eip)) )
+    case 0xea: /* jmp (far, absolute) */
+        ASSERT(!mode_64bit());
+        if ( (rc = load_seg(x86_seg_cs, imm2, 0, &cs, ctxt, ops)) ||
+             (rc = commit_far_branch(&cs, imm1)) )
             goto done;
         break;
-    }
 
     case 0xf1: /* int1 (icebp) */
         src.val = EXC_DB;