Re: [PATCH for-6.8 v3 1/3] LoongArch: KVM: Fix input validation of _kvm_get_cpucfg and kvm_check_cpucfg

[WANG Xuerui]

On 2/22/24 18:22, maobibo wrote:
> On 2024/2/22 下午5:45, WANG Xuerui wrote:
> > Hi,
> >
> > On 2/17/24 11:03, maobibo wrote:
> > > Hi Xuerui,
> > >
> > > Good catch, and thank for your patch.
> > >
> > > On 2024/2/16 下午4:58, WANG Xuerui wrote:
> > > > [snip]
> > > > @@ -324,31 +319,33 @@ static int _kvm_get_cpucfg(int id, u64 *v)
> > > >           if (cpu_has_lasx)
> > > >               *v |= CPUCFG2_LASX;
> > > > -        break;
> > > > +        return 0;
> > > > +    case 0 ... 1:
> > > > +    case 3 ... KVM_MAX_CPUCFG_REGS - 1:
> > > > +        /* no restrictions on other CPUCFG IDs' values */
> > > > +        *v = U64_MAX;
> > > > +        return 0;
> > > how about something like this?
> > >      default:
> > >          /* no restrictions on other CPUCFG IDs' values */
> > >          *v = U64_MAX;
> > >          return 0;
> >
> > I don't think this version correctly expresses the intent. Note that 
> > the CPUCFG ID range check is squashed into the switch as well, so one 
> > switch conveniently expresses the three intended cases at once:
> >
> > * the special treatment of CPUCFG2,
> +    case 0 ... 1:
> +    case 3 ... KVM_MAX_CPUCFG_REGS - 1:
> +        /* no restrictions on other CPUCFG IDs' values */
> +        *v = U64_MAX;
> +        return 0;
> cpucfg6 checking will be added for PMU support soon. So it will be
>          case 6:
>              do something check for cpucfg6
>              return mask;
>          case 0 ... 1:
>          case 3 ... 5:
>          case 7 ... KVM_MAX_CPUCFG_REGS - 1:
>                *v = U64_MAX;
>              return 0;
>
> If you think it is reasonable to add these separate "case" sentences, I 
> have no objection.
> > * all-allow rules for other in-range CPUCFG IDs, and
> > * rejection for out-of-range IDs.
>   static int kvm_check_cpucfg(int id, u64 val)
>   {
> -    u64 mask;
> -    int ret = 0;
> -
> -    if (id < 0 && id >= KVM_MAX_CPUCFG_REGS)
> -        return -EINVAL;
> you can modify && with ||, like this:
>      if (id < 0 || id >= KVM_MAX_CPUCFG_REGS)
>          return -EINVAL;

Yes I know. Personally I don't find the "three cases" that annoying, but 
I agree with you that it can be mildly frustrating if one case addition 
would split the ranges even more.

Given I'd like to also change the U64_MAX into U32_MAX (CPUCFG data is 
specified to be 32-bit wide), I'll send a v4 that keeps the "if" branch 
to make more people happy (Huacai privately also expressed preference 
for minimizing changes to the overall code shape). Thanks for your 
suggestion.

--
WANG "xen0n" Xuerui

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