[PATCH 0/4] x86: instruction emulator adjustments

[PATCH 0/4] x86: instruction emulator adjustments

[Jan Beulich]

1: support MOVBE and CRC32
2: use (locally) consistent exit mechanisms
3: drop pointless and add useful default cases
4: fold local variables

Patch 1 is a plain resend. Patch 2 is RFC (see there for a possible
alternative approach).

Signed-off-by: Jan Beulich <jbeulich@suse.com>


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[PATCH RESEND 1/4] x86emul: support MOVBE and CRC32

[Jan Beulich]

The former in an attempt to at least gradually support all simple data
movement instructions. The latter just because it shares the opcode
with the former.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -78,7 +78,14 @@ static int cpuid(
     unsigned int *edx,
     struct x86_emulate_ctxt *ctxt)
 {
+    unsigned int leaf = *eax;
+
     asm ("cpuid" : "+a" (*eax), "+c" (*ecx), "=d" (*edx), "=b" (*ebx));
+
+    /* The emulator doesn't itself use MOVBE, so we can always run the test. */
+    if ( leaf == 1 )
+        *ecx |= 1U << 22;
+
     return X86EMUL_OKAY;
 }
 
@@ -605,6 +612,34 @@ int main(int argc, char **argv)
     printf("skipped\n");
 #endif
 
+    printf("%-40s", "Testing movbe (%%ecx),%%eax...");
+    instr[0] = 0x0f; instr[1] = 0x38; instr[2] = 0xf0; instr[3] = 0x01;
+    regs.eflags = 0x200;
+    regs.eip    = (unsigned long)&instr[0];
+    regs.ecx    = (unsigned long)res;
+    regs.eax    = 0x11111111;
+    *res        = 0x12345678;
+    rc = x86_emulate(&ctxt, &emulops);
+    if ( (rc != X86EMUL_OKAY) ||
+         (*res != 0x12345678) ||
+         (regs.eax != 0x78563412) ||
+         (regs.eflags != 0x200) ||
+         (regs.eip != (unsigned long)&instr[4]) )
+        goto fail;
+    printf("okay\n");
+
+    printf("%-40s", "Testing movbe %%ax,(%%ecx)...");
+    instr[0] = 0x66; instr[1] = 0x0f; instr[2] = 0x38; instr[3] = 0xf1; instr[4] = 0x01;
+    regs.eip = (unsigned long)&instr[0];
+    rc = x86_emulate(&ctxt, &emulops);
+    if ( (rc != X86EMUL_OKAY) ||
+         (*res != 0x12341234) ||
+         (regs.eax != 0x78563412) ||
+         (regs.eflags != 0x200) ||
+         (regs.eip != (unsigned long)&instr[5]) )
+        goto fail;
+    printf("okay\n");
+
 #define decl_insn(which) extern const unsigned char which[], which##_len[]
 #define put_insn(which, insn) ".pushsection .test, \"ax\", @progbits\n" \
                               #which ": " insn "\n"                     \
--- a/tools/tests/x86_emulator/x86_emulate.c
+++ b/tools/tests/x86_emulator/x86_emulate.c
@@ -12,6 +12,7 @@ typedef bool bool_t;
 
 #define BUG() abort()
 #define ASSERT assert
+#define ASSERT_UNREACHABLE() assert(!__LINE__)
 
 #define cpu_has_amd_erratum(nr) 0
 #define mark_regs_dirty(r) ((void)(r))
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -12,6 +12,7 @@ CFLAGS += -msoft-float
 $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
 $(call cc-option-add,CFLAGS,CC,-Wnested-externs)
 $(call as-insn-check,CFLAGS,CC,"vmcall",-DHAVE_GAS_VMX)
+$(call as-insn-check,CFLAGS,CC,"crc32 %eax$$(comma)%eax",-DHAVE_GAS_SSE4_2)
 $(call as-insn-check,CFLAGS,CC,"invept (%rax)$$(comma)%rax",-DHAVE_GAS_EPT)
 $(call as-insn-check,CFLAGS,CC,"rdfsbase %rax",-DHAVE_GAS_FSGSBASE)
 $(call as-insn-check,CFLAGS,CC,".equ \"x\"$$(comma)1", \
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -188,7 +188,7 @@ static uint8_t twobyte_table[256] = {
     ImplicitOps, ImplicitOps, ImplicitOps, 0,
     ImplicitOps, ImplicitOps, 0, 0,
     /* 0x38 - 0x3F */
-    0, 0, 0, 0, 0, 0, 0, 0,
+    DstReg|SrcMem|ModRM, 0, 0, 0, 0, 0, 0, 0,
     /* 0x40 - 0x47 */
     DstReg|SrcMem|ModRM|Mov, DstReg|SrcMem|ModRM|Mov,
     DstReg|SrcMem|ModRM|Mov, DstReg|SrcMem|ModRM|Mov,
@@ -1098,6 +1098,8 @@ static bool_t vcpu_has(
 #define vcpu_must_have_sse2() vcpu_must_have(0x00000001, EDX, 26)
 #define vcpu_must_have_sse3() vcpu_must_have(0x00000001, ECX,  0)
 #define vcpu_must_have_cx16() vcpu_must_have(0x00000001, ECX, 13)
+#define vcpu_must_have_sse4_2() vcpu_must_have(0x00000001, ECX, 20)
+#define vcpu_must_have_movbe() vcpu_must_have(0x00000001, ECX, 22)
 #define vcpu_must_have_avx()  vcpu_must_have(0x00000001, ECX, 28)
 
 #ifdef __XEN__
@@ -1509,8 +1511,9 @@ x86_emulate(
     /* Shadow copy of register state. Committed on successful emulation. */
     struct cpu_user_regs _regs = *ctxt->regs;
 
-    uint8_t b, d, sib, sib_index, sib_base, twobyte = 0, rex_prefix = 0;
+    uint8_t b, d, sib, sib_index, sib_base, rex_prefix = 0;
     uint8_t modrm = 0, modrm_mod = 0, modrm_reg = 0, modrm_rm = 0;
+    enum { ext_none, ext_0f, ext_0f38 } ext = ext_none;
     union vex vex = {};
     unsigned int op_bytes, def_op_bytes, ad_bytes, def_ad_bytes;
     bool_t lock_prefix = 0;
@@ -1606,9 +1609,18 @@ x86_emulate(
         /* Two-byte opcode? */
         if ( b == 0x0f )
         {
-            twobyte = 1;
             b = insn_fetch_type(uint8_t);
             d = twobyte_table[b];
+            switch ( b )
+            {
+            default:
+                ext = ext_0f;
+                break;
+            case 0x38:
+                b = insn_fetch_type(uint8_t);
+                ext = ext_0f38;
+                break;
+            }
         }
 
         /* Unrecognised? */
@@ -1625,7 +1637,7 @@ x86_emulate(
         modrm = insn_fetch_type(uint8_t);
         modrm_mod = (modrm & 0xc0) >> 6;
 
-        if ( !twobyte && ((b & ~1) == 0xc4) )
+        if ( !ext && ((b & ~1) == 0xc4) )
             switch ( def_ad_bytes )
             {
             default:
@@ -1671,12 +1683,12 @@ x86_emulate(
                     rex_prefix |= REX_R;
 
                 fail_if(vex.opcx != vex_0f);
-                twobyte = 1;
+                ext = ext_0f;
                 b = insn_fetch_type(uint8_t);
                 d = twobyte_table[b];
 
                 /* Unrecognised? */
-                if ( d == 0 )
+                if ( d == 0 || b == 0x38 )
                     goto cannot_emulate;
 
                 modrm = insn_fetch_type(uint8_t);
@@ -1762,7 +1774,7 @@ x86_emulate(
                 {
                     ea.mem.seg  = x86_seg_ss;
                     ea.mem.off += _regs.esp;
-                    if ( !twobyte && (b == 0x8f) )
+                    if ( !ext && (b == 0x8f) )
                         /* POP <rm> computes its EA post increment. */
                         ea.mem.off += ((mode_64bit() && (op_bytes == 4))
                                        ? 8 : op_bytes);
@@ -1797,12 +1809,12 @@ x86_emulate(
                         ((op_bytes == 8) ? 4 : op_bytes);
                 else if ( (d & SrcMask) == SrcImmByte )
                     ea.mem.off += 1;
-                else if ( !twobyte && ((b & 0xfe) == 0xf6) &&
+                else if ( !ext && ((b & 0xfe) == 0xf6) &&
                           ((modrm_reg & 7) <= 1) )
                     /* Special case in Grp3: test has immediate operand. */
                     ea.mem.off += (d & ByteOp) ? 1
                         : ((op_bytes == 8) ? 4 : op_bytes);
-                else if ( twobyte && ((b & 0xf7) == 0xa4) )
+                else if ( ext == ext_0f && ((b & 0xf7) == 0xa4) )
                     /* SHLD/SHRD with immediate byte third operand. */
                     ea.mem.off++;
                 break;
@@ -1821,7 +1833,9 @@ x86_emulate(
         ea.mem.seg = override_seg;
 
     /* Early operand adjustments. */
-    if ( !twobyte )
+    switch ( ext )
+    {
+    case ext_none:
         switch ( b )
         {
         case 0xf6 ... 0xf7: /* Grp3 */
@@ -1854,6 +1868,29 @@ x86_emulate(
             }
             break;
         }
+        break;
+
+    case ext_0f:
+        break;
+
+    case ext_0f38:
+        switch ( b )
+        {
+        case 0xf0: /* movbe / crc32 */
+            d |= repne_prefix() ? ByteOp : Mov;
+            break;
+        case 0xf1: /* movbe / crc32 */
+            if ( !repne_prefix() )
+                d = (d & ~(DstMask | SrcMask)) | DstMem | SrcReg | Mov;
+            break;
+        default: /* Until it is worth making this table based ... */
+            goto cannot_emulate;
+        }
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+    }
 
     /* Decode and fetch the source operand: register, memory or immediate. */
     switch ( d & SrcMask )
@@ -2012,8 +2049,18 @@ x86_emulate(
         break;
     }
 
-    if ( twobyte )
-        goto twobyte_insn;
+    switch ( ext )
+    {
+    case ext_none:
+        break;
+    case ext_0f:
+        goto ext_0f_insn;
+    case ext_0f38:
+        goto ext_0f38_insn;
+    default:
+        ASSERT_UNREACHABLE();
+        goto cannot_emulate;
+    }
 
     switch ( b )
     {
@@ -2056,7 +2103,7 @@ x86_emulate(
         struct segment_register reg;
         src.val = x86_seg_es;
     push_seg:
-        generate_exception_if(mode_64bit() && !twobyte, EXC_UD, -1);
+        generate_exception_if(mode_64bit() && !ext, EXC_UD, -1);
         fail_if(ops->read_segment == NULL);
         if ( (rc = ops->read_segment(src.val, &reg, ctxt)) != 0 )
             return rc;
@@ -2072,7 +2119,7 @@ x86_emulate(
     case 0x07: /* pop %%es */
         src.val = x86_seg_es;
     pop_seg:
-        generate_exception_if(mode_64bit() && !twobyte, EXC_UD, -1);
+        generate_exception_if(mode_64bit() && !ext, EXC_UD, -1);
         fail_if(ops->write_segment == NULL);
         /* 64-bit mode: POP defaults to a 64-bit operand. */
         if ( mode_64bit() && (op_bytes == 4) )
@@ -2727,7 +2774,7 @@ x86_emulate(
         unsigned long sel;
         dst.val = x86_seg_es;
     les: /* dst.val identifies the segment */
-        generate_exception_if(mode_64bit() && !twobyte, EXC_UD, -1);
+        generate_exception_if(mode_64bit() && !ext, EXC_UD, -1);
         generate_exception_if(src.type != OP_MEM, EXC_UD, -1);
         if ( (rc = read_ulong(src.mem.seg, src.mem.off + src.bytes,
                               &sel, 2, ctxt, ops)) != 0 )
@@ -3865,7 +3912,7 @@ x86_emulate(
     put_stub(stub);
     return rc;
 
- twobyte_insn:
+ ext_0f_insn:
     switch ( b )
     {
     case 0x00: /* Grp6 */
@@ -4772,6 +4819,72 @@ x86_emulate(
     }
     goto writeback;
 
+ ext_0f38_insn:
+    switch ( b )
+    {
+    case 0xf0: case 0xf1: /* movbe / crc32 */
+        generate_exception_if(repe_prefix(), EXC_UD, -1);
+        if ( repne_prefix() )
+        {
+            /* crc32 */
+#ifdef HAVE_GAS_SSE4_2
+            host_and_vcpu_must_have(sse4_2);
+            dst.bytes = rex_prefix & REX_W ? 8 : 4;
+            switch ( op_bytes )
+            {
+            case 1:
+                asm ( "crc32b %1,%k0" : "+r" (dst.val)
+                                      : "qm" (*(uint8_t *)&src.val) );
+                break;
+            case 2:
+                asm ( "crc32w %1,%k0" : "+r" (dst.val)
+                                      : "rm" (*(uint16_t *)&src.val) );
+                break;
+            case 4:
+                asm ( "crc32l %1,%k0" : "+r" (dst.val)
+                                      : "rm" (*(uint32_t *)&src.val) );
+                break;
+# ifdef __x86_64__
+            case 8:
+                asm ( "crc32q %1,%0" : "+r" (dst.val) : "rm" (src.val) );
+                break;
+# endif
+            default:
+                ASSERT_UNREACHABLE();
+            }
+#else /* !HAVE_GAS_SSE4_2 */
+            goto cannot_emulate;
+#endif
+        }
+        else
+        {
+            /* movbe */
+            vcpu_must_have_movbe();
+            switch ( op_bytes )
+            {
+            case 2:
+                asm ( "xchg %h0,%b0" : "=Q" (dst.val)
+                                     : "0" (*(uint32_t *)&src.val) );
+                break;
+            case 4:
+#ifdef __x86_64__
+                asm ( "bswap %k0" : "=r" (dst.val)
+                                  : "0" (*(uint32_t *)&src.val) );
+                break;
+            case 8:
+#endif
+                asm ( "bswap %0" : "=r" (dst.val) : "0" (src.val) );
+                break;
+            default:
+                ASSERT_UNREACHABLE();
+            }
+        }
+        break;
+    default:
+        goto cannot_emulate;
+    }
+    goto writeback;
+
  cannot_emulate:
     _put_fpu();
     put_stub(stub);
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -57,6 +57,7 @@
 #define cpu_has_sse		boot_cpu_has(X86_FEATURE_SSE)
 #define cpu_has_sse2		boot_cpu_has(X86_FEATURE_SSE2)
 #define cpu_has_sse3		boot_cpu_has(X86_FEATURE_SSE3)
+#define cpu_has_sse4_2		boot_cpu_has(X86_FEATURE_SSE4_2)
 #define cpu_has_htt		boot_cpu_has(X86_FEATURE_HTT)
 #define cpu_has_nx		boot_cpu_has(X86_FEATURE_NX)
 #define cpu_has_clflush		boot_cpu_has(X86_FEATURE_CLFLUSH)



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Re: [PATCH RESEND 1/4] x86emul: support MOVBE and CRC32

[Andrew Cooper]

On 20/06/16 12:57, Jan Beulich wrote:
> The former in an attempt to at least gradually support all simple data
> movement instructions. The latter just because it shares the opcode
> with the former.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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[PATCH 2/4] x86emul: use (locally) consistent exit mechanisms

[Jan Beulich]

[-- Attachment #1: Type: text/plain, Size: 1476 bytes --]

At least similar code should use similar exit mechanisms (return vs
goto).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC reason: There are many more paths where we could return directly,
            avoiding the _put_fpu() and put_stub(). Otoh arguably the
            two existing return-s around the changes below could also
            be changed to "goto done" to restore consistency.

Subsequently we may then want to consider to reduce the number of
"goto done" by checking rc right after at least the main switch()
statements.

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2112,7 +2112,7 @@ x86_emulate(
             op_bytes = 8;
         if ( (rc = ops->write(x86_seg_ss, sp_pre_dec(op_bytes),
                               &reg.sel, op_bytes, ctxt)) != 0 )
-            goto done;
+            return rc;
         break;
     }
 
@@ -2125,9 +2125,8 @@ x86_emulate(
         if ( mode_64bit() && (op_bytes == 4) )
             op_bytes = 8;
         if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
-                              &dst.val, op_bytes, ctxt, ops)) != 0 )
-            goto done;
-        if ( (rc = load_seg(src.val, dst.val, 0, NULL, ctxt, ops)) != 0 )
+                              &dst.val, op_bytes, ctxt, ops)) != 0 ||
+             (rc = load_seg(src.val, dst.val, 0, NULL, ctxt, ops)) != 0 )
             return rc;
         break;
 




[-- Attachment #2: x86emul-consistently-bail.patch --]
[-- Type: text/plain, Size: 1523 bytes --]

x86emul: use (locally) consistent exit mechanisms

At least similar code should use similar exit mechanisms (return vs
goto).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC reason: There are many more paths where we could return directly,
            avoiding the _put_fpu() and put_stub(). Otoh arguably the
            two existing return-s around the changes below could also
            be changed to "goto done" to restore consistency.

Subsequently we may then want to consider to reduce the number of
"goto done" by checking rc right after at least the main switch()
statements.

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2112,7 +2112,7 @@ x86_emulate(
             op_bytes = 8;
         if ( (rc = ops->write(x86_seg_ss, sp_pre_dec(op_bytes),
                               &reg.sel, op_bytes, ctxt)) != 0 )
-            goto done;
+            return rc;
         break;
     }
 
@@ -2125,9 +2125,8 @@ x86_emulate(
         if ( mode_64bit() && (op_bytes == 4) )
             op_bytes = 8;
         if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
-                              &dst.val, op_bytes, ctxt, ops)) != 0 )
-            goto done;
-        if ( (rc = load_seg(src.val, dst.val, 0, NULL, ctxt, ops)) != 0 )
+                              &dst.val, op_bytes, ctxt, ops)) != 0 ||
+             (rc = load_seg(src.val, dst.val, 0, NULL, ctxt, ops)) != 0 )
             return rc;
         break;
 

[-- Attachment #3: Type: text/plain, Size: 126 bytes --]

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Re: [PATCH 2/4] x86emul: use (locally) consistent exit mechanisms

[Andrew Cooper]

On 20/06/16 12:58, Jan Beulich wrote:
> At least similar code should use similar exit mechanisms (return vs
> goto).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> RFC reason: There are many more paths where we could return directly,
>             avoiding the _put_fpu() and put_stub(). Otoh arguably the
>             two existing return-s around the changes below could also
>             be changed to "goto done" to restore consistency.
>
> Subsequently we may then want to consider to reduce the number of
> "goto done" by checking rc right after at least the main switch()
> statements.

I think this patch goes in the wrong direction.  Mixing exit mechanisms
makes code harder to interpret, and x86_emulate() isn't the easiest
function to edit.

Using "goto done;" consistently would be a better option.

~Andrew

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Re: [PATCH 2/4] x86emul: use (locally) consistent exit mechanisms

[Jan Beulich]

>>> On 23.06.16 at 12:36, <andrew.cooper3@citrix.com> wrote:
> On 20/06/16 12:58, Jan Beulich wrote:
>> At least similar code should use similar exit mechanisms (return vs
>> goto).
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> RFC reason: There are many more paths where we could return directly,
>>             avoiding the _put_fpu() and put_stub(). Otoh arguably the
>>             two existing return-s around the changes below could also
>>             be changed to "goto done" to restore consistency.
>>
>> Subsequently we may then want to consider to reduce the number of
>> "goto done" by checking rc right after at least the main switch()
>> statements.
> 
> I think this patch goes in the wrong direction.  Mixing exit mechanisms
> makes code harder to interpret, and x86_emulate() isn't the easiest
> function to edit.

Well, that's what I had put up in the RFC remark. I'm all for
consistency, what I'm not sure is whether this ...

> Using "goto done;" consistently would be a better option.

is better than (always) using plain return where possible.

Jan


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[PATCH 3/4] x86emul: drop pointless and add useful default cases

[Jan Beulich]

[-- Attachment #1: Type: text/plain, Size: 2392 bytes --]

There's no point in having default cases when all possible values have
respective case statements, or when there's just a "break" statement.

Otoh the two main switch() statements better get default cases added,
just to cover the case of someone altering one of the two lookup arrays
without suitably changing these switch statements.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1379,7 +1379,6 @@ decode_segment(uint8_t modrm_reg)
     case 3: return x86_seg_ds;
     case 4: return x86_seg_fs;
     case 5: return x86_seg_gs;
-    default: break;
     }
     return decode_segment_failed;
 }
@@ -2996,8 +2995,6 @@ x86_emulate(
             case 7: /* fdivr */
                 emulate_fpu_insn_memsrc("fdivrs", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3128,8 +3125,6 @@ x86_emulate(
             case 7: /* fidivr m32i */
                 emulate_fpu_insn_memsrc("fidivrl", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3352,8 +3347,6 @@ x86_emulate(
             case 7: /* fidivr m16i */
                 emulate_fpu_insn_memsrc("fidivrs", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3431,8 +3424,6 @@ x86_emulate(
                 dst.type = OP_MEM;
                 emulate_fpu_insn_memdst("fistpll", dst.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3750,8 +3741,6 @@ x86_emulate(
             }
             break;
         }
-        default:
-            goto cannot_emulate;
         }
         break;
 
@@ -3845,10 +3834,11 @@ x86_emulate(
             goto push;
         case 7:
             generate_exception_if(1, EXC_UD, -1);
-        default:
-            goto cannot_emulate;
         }
         break;
+
+    default:
+        BUG();
     }
 
  writeback:
@@ -4815,6 +4805,9 @@ x86_emulate(
             break;
         }
         break;
+
+    default:
+        BUG();
     }
     goto writeback;
 




[-- Attachment #2: x86emul-default-cases.patch --]
[-- Type: text/plain, Size: 2442 bytes --]

x86emul: drop pointless and add useful default cases

There's no point in having default cases when all possible values have
respective case statements, or when there's just a "break" statement.

Otoh the two main switch() statements better get default cases added,
just to cover the case of someone altering one of the two lookup arrays
without suitably changing these switch statements.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1379,7 +1379,6 @@ decode_segment(uint8_t modrm_reg)
     case 3: return x86_seg_ds;
     case 4: return x86_seg_fs;
     case 5: return x86_seg_gs;
-    default: break;
     }
     return decode_segment_failed;
 }
@@ -2996,8 +2995,6 @@ x86_emulate(
             case 7: /* fdivr */
                 emulate_fpu_insn_memsrc("fdivrs", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3128,8 +3125,6 @@ x86_emulate(
             case 7: /* fidivr m32i */
                 emulate_fpu_insn_memsrc("fidivrl", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3352,8 +3347,6 @@ x86_emulate(
             case 7: /* fidivr m16i */
                 emulate_fpu_insn_memsrc("fidivrs", src.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3431,8 +3424,6 @@ x86_emulate(
                 dst.type = OP_MEM;
                 emulate_fpu_insn_memdst("fistpll", dst.val);
                 break;
-            default:
-                goto cannot_emulate;
             }
         }
         break;
@@ -3750,8 +3741,6 @@ x86_emulate(
             }
             break;
         }
-        default:
-            goto cannot_emulate;
         }
         break;
 
@@ -3845,10 +3834,11 @@ x86_emulate(
             goto push;
         case 7:
             generate_exception_if(1, EXC_UD, -1);
-        default:
-            goto cannot_emulate;
         }
         break;
+
+    default:
+        BUG();
     }
 
  writeback:
@@ -4815,6 +4805,9 @@ x86_emulate(
             break;
         }
         break;
+
+    default:
+        BUG();
     }
     goto writeback;
 

[-- Attachment #3: Type: text/plain, Size: 126 bytes --]

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Re: [PATCH 3/4] x86emul: drop pointless and add useful default cases

[Andrew Cooper]

On 20/06/16 12:58, Jan Beulich wrote:
> @@ -3845,10 +3834,11 @@ x86_emulate(
>              goto push;
>          case 7:
>              generate_exception_if(1, EXC_UD, -1);
> -        default:
> -            goto cannot_emulate;
>          }
>          break;
> +
> +    default:
> +        BUG();

These introduce DoS vulnerabilities if there is indeed a path to default.

Could I recommend instead a one-time printk() dumping the instruction
stream which lead to here, an ASSERT_UNREACHABLE(), and a goto
cannot_emulate?

That way, a production build won't crash.

~Andrew

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Re: [PATCH 3/4] x86emul: drop pointless and add useful default cases

[Jan Beulich]

>>> On 23.06.16 at 12:44, <andrew.cooper3@citrix.com> wrote:
> On 20/06/16 12:58, Jan Beulich wrote:
>> @@ -3845,10 +3834,11 @@ x86_emulate(
>>              goto push;
>>          case 7:
>>              generate_exception_if(1, EXC_UD, -1);
>> -        default:
>> -            goto cannot_emulate;
>>          }
>>          break;
>> +
>> +    default:
>> +        BUG();
> 
> These introduce DoS vulnerabilities if there is indeed a path to default.
> 
> Could I recommend instead a one-time printk() dumping the instruction
> stream which lead to here, an ASSERT_UNREACHABLE(), and a goto
> cannot_emulate?
> 
> That way, a production build won't crash.

Good point, will do.

Jan


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[PATCH 4/4] x86emul: fold local variables

[Jan Beulich]

[-- Attachment #1: Type: text/plain, Size: 2723 bytes --]

Declare some variables to they can be used by multiple pieces of code,
allowing some figure braces to be dropped (which don't align nicely
when used inside of case labeled statements).

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3548,6 +3548,8 @@ x86_emulate(
     case 0xf6 ... 0xf7: /* Grp3 */
         switch ( modrm_reg & 7 )
         {
+            unsigned long u[2], v;
+
         case 0 ... 1: /* test */
             goto test;
         case 2: /* not */
@@ -3586,15 +3588,15 @@ x86_emulate(
                 _regs.edx = (uint32_t)(dst.val >> 32);
                 break;
 #endif
-            default: {
-                unsigned long m[2] = { src.val, dst.val };
-                if ( mul_dbl(m) )
+            default:
+                u[0] = src.val;
+                u[1] = dst.val;
+                if ( mul_dbl(u) )
                     _regs.eflags |= EFLG_OF|EFLG_CF;
-                _regs.edx = m[1];
-                dst.val  = m[0];
+                _regs.edx = u[1];
+                dst.val  = u[0];
                 break;
             }
-            }
             break;
         case 5: /* imul */
             dst.type = OP_REG;
@@ -3630,20 +3632,18 @@ x86_emulate(
                     _regs.edx = (uint32_t)(dst.val >> 32);
                 break;
 #endif
-            default: {
-                unsigned long m[2] = { src.val, dst.val };
-                if ( imul_dbl(m) )
+            default:
+                u[0] = src.val;
+                u[1] = dst.val;
+                if ( imul_dbl(u) )
                     _regs.eflags |= EFLG_OF|EFLG_CF;
                 if ( b > 0x6b )
-                    _regs.edx = m[1];
-                dst.val  = m[0];
+                    _regs.edx = u[1];
+                dst.val  = u[0];
                 break;
             }
-            }
             break;
-        case 6: /* div */ {
-            unsigned long u[2], v;
-
+        case 6: /* div */
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             switch ( dst.bytes = src.bytes )
@@ -3690,10 +3690,7 @@ x86_emulate(
                 break;
             }
             break;
-        }
-        case 7: /* idiv */ {
-            unsigned long u[2], v;
-
+        case 7: /* idiv */
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             switch ( dst.bytes = src.bytes )
@@ -3741,7 +3738,6 @@ x86_emulate(
             }
             break;
         }
-        }
         break;
 
     case 0xf8: /* clc */




[-- Attachment #2: x86emul-fold-locals.patch --]
[-- Type: text/plain, Size: 2750 bytes --]

x86emul: fold local variables

Declare some variables to they can be used by multiple pieces of code,
allowing some figure braces to be dropped (which don't align nicely
when used inside of case labeled statements).

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3548,6 +3548,8 @@ x86_emulate(
     case 0xf6 ... 0xf7: /* Grp3 */
         switch ( modrm_reg & 7 )
         {
+            unsigned long u[2], v;
+
         case 0 ... 1: /* test */
             goto test;
         case 2: /* not */
@@ -3586,15 +3588,15 @@ x86_emulate(
                 _regs.edx = (uint32_t)(dst.val >> 32);
                 break;
 #endif
-            default: {
-                unsigned long m[2] = { src.val, dst.val };
-                if ( mul_dbl(m) )
+            default:
+                u[0] = src.val;
+                u[1] = dst.val;
+                if ( mul_dbl(u) )
                     _regs.eflags |= EFLG_OF|EFLG_CF;
-                _regs.edx = m[1];
-                dst.val  = m[0];
+                _regs.edx = u[1];
+                dst.val  = u[0];
                 break;
             }
-            }
             break;
         case 5: /* imul */
             dst.type = OP_REG;
@@ -3630,20 +3632,18 @@ x86_emulate(
                     _regs.edx = (uint32_t)(dst.val >> 32);
                 break;
 #endif
-            default: {
-                unsigned long m[2] = { src.val, dst.val };
-                if ( imul_dbl(m) )
+            default:
+                u[0] = src.val;
+                u[1] = dst.val;
+                if ( imul_dbl(u) )
                     _regs.eflags |= EFLG_OF|EFLG_CF;
                 if ( b > 0x6b )
-                    _regs.edx = m[1];
-                dst.val  = m[0];
+                    _regs.edx = u[1];
+                dst.val  = u[0];
                 break;
             }
-            }
             break;
-        case 6: /* div */ {
-            unsigned long u[2], v;
-
+        case 6: /* div */
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             switch ( dst.bytes = src.bytes )
@@ -3690,10 +3690,7 @@ x86_emulate(
                 break;
             }
             break;
-        }
-        case 7: /* idiv */ {
-            unsigned long u[2], v;
-
+        case 7: /* idiv */
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             switch ( dst.bytes = src.bytes )
@@ -3741,7 +3738,6 @@ x86_emulate(
             }
             break;
         }
-        }
         break;
 
     case 0xf8: /* clc */

[-- Attachment #3: Type: text/plain, Size: 126 bytes --]

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Re: [PATCH 4/4] x86emul: fold local variables

[Andrew Cooper]

[-- Attachment #1.1: Type: text/plain, Size: 336 bytes --]

On 20/06/16 12:59, Jan Beulich wrote:
> Declare some variables to they can be used by multiple pieces of code,
> allowing some figure braces to be dropped (which don't align nicely
> when used inside of case labeled statements).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

[-- Attachment #1.2: Type: text/html, Size: 887 bytes --]

[-- Attachment #2: Type: text/plain, Size: 126 bytes --]

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