Re: [Xen-devel] [PATCH v4 6/6] x86emul: improve CR/DR access handling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/01/17 09:06, Jan Beulich wrote:
> - don't accept LOCK for DR accesses (it's undefined in the manuals)
> - only accept LOCK for CR accesses when the respective feature flag is
>   set (which would not normally be the case for Intel)
> - add (rather than or) 8 when LOCK is present; real hardware #UDs
>   when both REX.W and LOCK are present, implying that these would
>   rather access hypothetical CR16...23
> - eliminate explicit decode_register() calls
> - streamline remaining read/write code
>
> No further functional change, i.e. not addressing the missing exception
> generation (#UD for invalid CR/DR encodings, #GP(0) for invalid write
> values, #DB for DR accesses with DR7.GD set).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -194,7 +194,8 @@ static const opcode_desc_t twobyte_table
>      ImplicitOps|ModRM, ImplicitOps|ModRM, ImplicitOps|ModRM, 
> ImplicitOps|ModRM,
>      ImplicitOps|ModRM, ImplicitOps|ModRM, ImplicitOps|ModRM, 
> ImplicitOps|ModRM,
>      /* 0x20 - 0x27 */
> -    ImplicitOps|ModRM, ImplicitOps|ModRM, ImplicitOps|ModRM, 
> ImplicitOps|ModRM,
> +    DstMem|SrcImplicit|ModRM, DstMem|SrcImplicit|ModRM,
> +    DstImplicit|SrcMem|ModRM, DstImplicit|SrcMem|ModRM,

These are Src/Dst Reg rather than Mem, although its not immediately
obvious how this would alter the outcome.

Everything else looks fine though.

~Andrew

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