Re: [Xen-devel] [PATCH] x86emul: don't allow null selector for LTR

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Sep 22, 2016 at 12:38:22AM -0600, Jan Beulich wrote:
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> This goes on top of
> https://lists.xenproject.org/archives/html/xen-devel/2016-09/msg02198.html 
> 
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -1207,10 +1207,17 @@ protmode_load_seg(
>      /* NULL selector? */
>      if ( (sel & 0xfffc) == 0 )
>      {
> -        if ( (seg == x86_seg_cs) ||
> -             ((seg == x86_seg_ss) &&
> -              (!mode_64bit() || (cpl == 3) || (cpl != sel))) )
> +        switch ( seg )
> +        {
> +        case x86_seg_ss:
> +            if ( mode_64bit() && (cpl != 3) && (cpl == sel) )
> +        default:
> +                break;
> +            /* fall through */
> +        case x86_seg_cs:
> +        case x86_seg_tr:
>              goto raise_exn;
> +        }
>          memset(sreg, 0, sizeof(*sreg));
>          sreg->sel = sel;
>          return X86EMUL_OKAY;
> 

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