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

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Message-ID: <1469010283.2800.5.camel@gmail.com>
Date:	Wed, 20 Jul 2016 20:24:43 +1000
From:	Balbir Singh <bsingharora@...il.com>
To:	Kees Cook <keescook@...omium.org>,
	Laura Abbott <labbott@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Daniel Micay <danielmicay@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
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	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 02/11] mm: Hardened usercopy

On Tue, 2016-07-19 at 11:48 -0700, Kees Cook wrote:
> On Mon, Jul 18, 2016 at 6:06 PM, Laura Abbott <labbott@...hat.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.