Re: [PATCHv2 1/6] KVM: emulator: drop RPL check from linearize() function

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-12-20 15:57, Gleb Natapov wrote:
> According to Intel SDM Vol3 Section 5.5 "Privilege Levels" and 5.6
> "Privilege Level Checking When Accessing Data Segments" RPL checking is
> done during loading of a segment selector, not during data access. We
> already do checking during segment selector loading, so drop the check
> during data access. Checking RPL during data access triggers #GP if
> after transition from real mode to protected mode RPL bits in a segment
> selector are set.
> 
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
>  arch/x86/kvm/emulate.c |    7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index c7547b3..a3d31e3 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -665,7 +665,7 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
>  	ulong la;
>  	u32 lim;
>  	u16 sel;
> -	unsigned cpl, rpl;
> +	unsigned cpl;
>  
>  	la = seg_base(ctxt, addr.seg) + addr.ea;
>  	switch (ctxt->mode) {
> @@ -699,11 +699,6 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
>  				goto bad;
>  		}
>  		cpl = ctxt->ops->cpl(ctxt);
> -		if (ctxt->mode == X86EMUL_MODE_REAL)
> -			rpl = 0;
> -		else
> -			rpl = sel & 3;
> -		cpl = max(cpl, rpl);
>  		if (!(desc.type & 8)) {
>  			/* data segment */
>  			if (cpl > desc.dpl)
> 

I suppose this one is queued for 3.8 and stable already, right? We
happen to hit the case reliably while booting an older SUSE guest on an
AMD host.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux