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From: Balbir Singh <bsingharora@gmail.com>
Date: Wed, 20 Jul 2016 20:24:43 +1000
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Subject: [kernel-hardening] Re: [PATCH v3 02/11] mm: Hardened usercopy
To: Kees Cook <keescook@chromium.org>, Laura Abbott <labbott@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Daniel Micay <danielmicay@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Rik van Riel <riel@redhat.com>, Casey Schaufler <casey@schaufler-ca.com>, PaX Team <pageexec@freemail.hu>, Brad Spengler <spender@grsecurity.net>, Russell King <linux@armlinux.org.uk>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Michael Ellerman <mpe@ellerman.id.au>, Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>, "David S.
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On Tue, 2016-07-19 at 11:48 -0700, Kees Cook wrote:
> On Mon, Jul 18, 2016 at 6:06 PM, Laura Abbott <labbott@redhat.com> 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.