linux-kernel - Re: [PATCH v2 02/11] mm: Hardened usercopy

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Message-ID: <1468544658.30053.26.camel@redhat.com>
Date:	Thu, 14 Jul 2016 21:04:18 -0400
From:	Rik van Riel <riel@...hat.com>
To:	bsingharora@...il.com, Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	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>,
	Michael Ellerman <mpe@...erman.id.au>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"David S. Miller" <davem@...emloft.net>, x86@...nel.org,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Mathias Krause <minipli@...glemail.com>,
	Jan Kara <jack@...e.cz>, Vitaly Wool <vitalywool@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Laura Abbott <labbott@...oraproject.org>,
	linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 02/11] mm: Hardened usercopy

On Fri, 2016-07-15 at 09:20 +1000, Balbir Singh wrote:

> > ==
> > +		   ((unsigned long)end & (unsigned
> > long)PAGE_MASK)))
> > +		return NULL;
> > +
> > +	/* Allow if start and end are inside the same compound
> > page. */
> > +	endpage = virt_to_head_page(end);
> > +	if (likely(endpage == page))
> > +		return NULL;
> > +
> > +	/* Allow special areas, device memory, and sometimes
> > kernel data. */
> > +	if (PageReserved(page) && PageReserved(endpage))
> > +		return NULL;
> 
> If we came here, it's likely that endpage > page, do we need to check
> that only the first and last pages are reserved? What about the ones
> in
> the middle?

I think this will be so rare, we can get away with just
checking the beginning and the end.

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