Re: [Xen-devel] [PATCH v2] x86emul/fuzz: add a state sanitization function

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.04.19 at 12:44, <George.Dunlap@xxxxxxxxxx> wrote:
>> On Apr 1, 2019, at 8:46 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> +/*
>> + * Call this function from hooks potentially altering machine state into
>> + * something that's not architecturally valid, yet which - as per above -
>> + * the emulator relies on.
>> + */
>> +static bool sanitize_state(struct x86_emulate_ctxt *ctxt)
>> +{
>> +    const struct fuzz_state *s = ctxt->data;
>> +    const struct fuzz_corpus *c = s->corpus;
>> +    const struct cpu_user_regs *regs = &c->regs;
>> +
>> +    if ( long_mode_active(ctxt) && !(c->cr[0] & X86_CR0_PG) )
>> +        return false;
>> +
>> +    if ( (c->cr[0] & X86_CR0_PG) && !(c->cr[0] & X86_CR0_PE) )
>> +        return false;
>> +
>> +    if ( (regs->rflags & X86_EFLAGS_VM) &&
>> +         (c->segments[x86_seg_cs].db || c->segments[x86_seg_ss].db) )
>> +        return false;
>> +
>> +    return true;
>> +}
> 
> Sorry, I didn’t read this function very well on Friday.  It’s not actually 
> doing any sanitation; rather, it’s checking whether the state is 
> architecturally valid.  Or more precisely: it’s checking whether the 
> emulator's assumptions about the state still hold.
> 
> check_state?  sanity_check_state?  

Hmm, yes - initially I was meaning to alter state, and then I decided
differently but didn't change the name. I'll go with check_state().

Jan


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