Re: [PATCH v3 02/11] mm: Hardened usercopy

[Laura Abbott]

On 07/20/2016 03:24 AM, Balbir Singh wrote:
> On Tue, 2016-07-19 at 11:48 -0700, Kees Cook wrote:
> > On Mon, Jul 18, 2016 at 6:06 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> > > On 07/15/2016 02:44 PM, Kees Cook wrote:
> > >
> > > This doesn't work when copying CMA allocated memory since CMA purposely
> > > allocates larger than a page block size without setting head pages.
> > > Given CMA may be used with drivers doing zero copy buffers, I think it
> > > should be permitted.
> > >
> > > Something like the following lets it pass (I can clean up and submit
> > > the is_migrate_cma_page APIs as a separate patch for review)
> > Yeah, this would be great. I'd rather use an accessor to check this
> > than a direct check for MIGRATE_CMA.
> >
> > >          */
> > >         for (; ptr <= end ; ptr += PAGE_SIZE, page = virt_to_head_page(ptr))
> > > {
> > > -               if (!PageReserved(page))
> > > +               if (!PageReserved(page) && !is_migrate_cma_page(page))
> > >                         return "<spans multiple pages>";
> > >         }
> > Yeah, I'll modify this a bit so that which type it starts as is
> > maintained for all pages (rather than allowing to flip back and forth
> > -- even though that is likely impossible).
> Sorry, I completely missed the MIGRATE_CMA bits. Could you clarify if you
> caught this in testing/review?
>
> Balbir Singh.

I caught it while looking at the code and then wrote a test case to confirm
I was correct because I wasn't sure how to easily find an in tree user.

Thanks,
Laura