Re: [Xen-devel] [PATCH v5 6/8] xen/arm: introduce GNTTABOP_cache_flush

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 16 Oct 2014, Jan Beulich wrote:
> >>> On 16.10.14 at 12:55, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > On Tue, 14 Oct 2014, Jan Beulich wrote:
> >> >>> On 13.10.14 at 16:58, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> > +static bool_t grant_map_exists(const struct domain *ld,
> >> > +                        struct grant_table *rgt,
> >> > +                        unsigned long mfn)
> >> > +{
> >> > +    const struct active_grant_entry *act;
> >> > +    grant_ref_t ref;
> >> > +
> >> > +    ASSERT(spin_is_locked(&rgt->lock));
> >> > +
> >> > +    for ( ref = 0; ref != nr_grant_entries(rgt); ref++ )
> >> 
> >> Unless I overlooked something here or in an earlier patch I think
> >> you're _still_ not enforcing a suitably low upper limit on the
> >> variable that controls the maximum iteration count here. Whether
> >> you enforce this the hard way (by just capping an eventual
> >> command line specified value) or the soft way (by issuing a
> >> warning that such a setting may hamper security, plus
> >> documenting the supported value range) is up to you.
> > 
> > What value range do you suggest?
> 
> Whatever is suitable to limit the loop to no more than a few thousand
> iterations.

To limit the number of iterations to 5000, we need 10 grant frames max.
I'll use that as limit, that also means changing
DEFAULT_MAX_NR_GRANT_FRAMES to 10.

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