Re: [PATCH 2/5] KVM: x86: Emulator performs code segment checks on read access

["Radim Krčmář" <rkrcmar@redhat.com>]

2014-10-03 01:10+0300, Nadav Amit:
> When read access is performed using a readable code segment, the "conforming"
> and "non-conforming" checks should not be done.  As a result, read using
> non-conforming readable code segment fails.
> 
> This is according to Intel SDM 5.6.1 ("Accessing Data in Code Segments").

(Checks are neccessarily true, except for non-conforming readable code,
 which is to be treated like a data segment.)

> The fix is not to perform the "non-conforming" checks if the access is not a
> fetch.

(Because 'fetch' implies correct conditions and the rest is checked when
 loading the segment,)

> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
> ---

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>

>  arch/x86/kvm/emulate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index a46207a..694dfa7 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -661,8 +661,8 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
>  				goto bad;
>  		}
>  		cpl = ctxt->ops->cpl(ctxt);
> -		if (!(desc.type & 8)) {
> -			/* data segment */
> +		if (!fetch) {
> +			/* data segment or readable code segment */
>  			if (cpl > desc.dpl)
>  				goto bad;
>  		} else if ((desc.type & 8) && !(desc.type & 4)) {
> -- 
> 1.9.1
> 
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