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

[Gleb Natapov <gleb@redhat.com>]

On Mon, Feb 11, 2013 at 05:58:24PM +0100, Jan Kiszka wrote:
> 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.
> 
The patch was in the middle of the pile of vmx real mode fixes. I had
no reports that it can be triggered on its own, so it was not queued
neither to 3.8 nor to stable. Is it a regression?  If yes what version
the bug appears in?

--
			Gleb.