Re: KVM: x86: use proper port value when checking io instruction permission

[Avi Kivity <avi@redhat.com>]

On 05/24/2011 08:27 PM, Gleb Natapov wrote:
> On Tue, May 24, 2011 at 02:11:20PM -0300, Marcelo Tosatti wrote:
> >
> >  Commit fa4491a6b667304 moved the permission check for io instructions
> >  to the ->check_perm callback. It failed to copy the port value from RDX
> >  register for string and "in,out ax,dx" instructions. Fix it.
> >
> >  Fixes FC8.32 installation.

Ouch.


> >  @@ -2955,6 +2964,15 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
> >   {
> >   	struct decode_cache *c =&ctxt->decode;
> >
> >  +	switch (c->b) {
> >  +	case 0x6e: /* outsb */
> >  +	case 0x6f: /* outsw/outsd */
> >  +	case 0xee: /* out dx,al */
> >  +	case 0xef: /* out dx,(e/r)ax */
> >  +		c->dst.val = c->regs[VCPU_REGS_RDX];
> >  +		break;
> >  +	}
> >  +
> >   	c->src.bytes = min(c->src.bytes, 4u);
> >   	if (!emulator_io_permited(ctxt, c->dst.val, c->src.bytes))
> >   		return emulate_gp(ctxt, 0);
> I'd rather do it at decoding stage by adding SrcDX/DstDX.
>

Note we haven't decoded operands yet.  And this doesn't fix in $imm8, %al.

Maybe we need an additional check site after operands are fetched.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.