Re: [PATCH v2 02/11] mm: Hardened usercopy
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- To: Rik van Riel <riel@xxxxxxxxxx>
- Subject: Re: [PATCH v2 02/11] mm: Hardened usercopy
- From: Balbir Singh <bsingharora@xxxxxxxxx>
- Date: Fri, 15 Jul 2016 11:41:51 +1000
- Cc: bsingharora@xxxxxxxxx, Kees Cook <keescook@xxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Casey Schaufler <casey@xxxxxxxxxxxxxxxx>, PaX Team <pageexec@xxxxxxxxxxx>, Brad Spengler <spender@xxxxxxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, x86@xxxxxxxxxx, Christoph Lameter <cl@xxxxxxxxx>, Pekka Enberg <penberg@xxxxxxxxxx>, David Rientjes <rientjes@xxxxxxxxxx>, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Mathias Krause <minipli@xxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Vitaly Wool <vitalywool@xxxxxxxxx>, Andrea Arcangeli <aarcange@xxxxxxxxxx>, Dmitry Vyukov <dvyukov@xxxxxxxxxx>, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, kernel-hardening@xxxxxxxxxxxxxxxxxx
- In-reply-to: <1468544658.30053.26.camel@redhat.com>
- List-id: <linux-ia64.vger.kernel.org>
- References: <1468446964-22213-1-git-send-email-keescook@chromium.org> <1468446964-22213-3-git-send-email-keescook@chromium.org> <20160714232019.GA28254@350D> <1468544658.30053.26.camel@redhat.com>
- Reply-to: bsingharora@xxxxxxxxx
- User-agent: Mutt/1.6.1 (2016-04-27)
On Thu, Jul 14, 2016 at 09:04:18PM -0400, Rik van Riel wrote:
> 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.
>
But do we want to leave a hole where an aware user space
can try a longer copy_* to avoid this check? If it is unlikely
should we just bite the bullet and do the check for the entire
range?
Balbir Singh.
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