[PATCH] x86emul: tighten CLFLUSH emulation

[PATCH] x86emul: tighten CLFLUSH emulation

[Jan Beulich]

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While for us it's not as bad as it was for Linux, their commit
13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
a memory mode (otherwise it's SFENCE) and when there's no REP prefix
(an operand size prefix is fine, as that's CLFLUSHOPT).

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
@@ -4400,7 +4400,9 @@ x86_emulate(
     case 0xae: /* Grp15 */
         switch ( modrm_reg & 7 )
         {
-        case 7: /* clflush */
+        case 7: /* clflush{,opt} */
+            fail_if(modrm_mod == 3);
+            fail_if(rep_prefix());
             fail_if(ops->wbinvd == NULL);
             if ( (rc = ops->wbinvd(ctxt)) != 0 )
                 goto done;




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x86emul: tighten CLFLUSH emulation

While for us it's not as bad as it was for Linux, their commit
13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
a memory mode (otherwise it's SFENCE) and when there's no REP prefix
(an operand size prefix is fine, as that's CLFLUSHOPT).

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
@@ -4400,7 +4400,9 @@ x86_emulate(
     case 0xae: /* Grp15 */
         switch ( modrm_reg & 7 )
         {
-        case 7: /* clflush */
+        case 7: /* clflush{,opt} */
+            fail_if(modrm_mod == 3);
+            fail_if(rep_prefix());
             fail_if(ops->wbinvd == NULL);
             if ( (rc = ops->wbinvd(ctxt)) != 0 )
                 goto done;

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Re: [PATCH] x86emul: tighten CLFLUSH emulation

[Andrew Cooper]

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On 12/01/15 08:23, Jan Beulich wrote:
> While for us it's not as bad as it was for Linux, their commit
> 13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
> Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
> shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
> a memory mode (otherwise it's SFENCE) and when there's no REP prefix
> (an operand size prefix is fine, as that's CLFLUSHOPT).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

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

>
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -4400,7 +4400,9 @@ x86_emulate(
>      case 0xae: /* Grp15 */
>          switch ( modrm_reg & 7 )
>          {
> -        case 7: /* clflush */
> +        case 7: /* clflush{,opt} */
> +            fail_if(modrm_mod == 3);
> +            fail_if(rep_prefix());
>              fail_if(ops->wbinvd == NULL);
>              if ( (rc = ops->wbinvd(ctxt)) != 0 )
>                  goto done;
>
>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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