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Date: Thu, 7 Jul 2016 09:30:07 +0200
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc: 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>,
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 0/9] mm: Hardened usercopy
On 07/07/2016 12:25 AM, Kees Cook wrote:
> Hi,
>
> This is a start of the mainline port of PAX_USERCOPY[1]. After I started
> writing tests (now in lkdtm in -next) for Casey's earlier port[2], I
> kept tweaking things further and further until I ended up with a whole
> new patch series. To that end, I took Rik's feedback and made a number
> of other changes and clean-ups as well.
>
> Based on my understanding, PAX_USERCOPY was designed to catch a few
> classes of flaws around the use of copy_to_user()/copy_from_user(). These
> changes don't touch get_user() and put_user(), since these operate on
> constant sized lengths, and tend to be much less vulnerable. There
> are effectively three distinct protections in the whole series,
> each of which I've given a separate CONFIG, though this patch set is
> only the first of the three intended protections. (Generally speaking,
> PAX_USERCOPY covers what I'm calling CONFIG_HARDENED_USERCOPY (this) and
> CONFIG_HARDENED_USERCOPY_WHITELIST (future), and PAX_USERCOPY_SLABS covers
> CONFIG_HARDENED_USERCOPY_SPLIT_KMALLOC (future).)
>
> This series, which adds CONFIG_HARDENED_USERCOPY, checks that objects
> being copied to/from userspace meet certain criteria:
> - if address is a heap object, the size must not exceed the object's
> allocated size. (This will catch all kinds of heap overflow flaws.)
> - if address range is in the current process stack, it must be within the
> current stack frame (if such checking is possible) or at least entirely
> within the current process's stack. (This could catch large lengths that
> would have extended beyond the current process stack, or overflows if
> their length extends back into the original stack.)
> - if the address range is part of kernel data, rodata, or bss, allow it.
> - if address range is page-allocated, that it doesn't span multiple
> allocations.
> - if address is within the kernel text, reject it.
> - everything else is accepted
>
> The patches in the series are:
> - The core copy_to/from_user() checks, without the slab object checks:
> 1- mm: Hardened usercopy
> - Per-arch enablement of the protection:
> 2- x86/uaccess: Enable hardened usercopy
> 3- ARM: uaccess: Enable hardened usercopy
> 4- arm64/uaccess: Enable hardened usercopy
> 5- ia64/uaccess: Enable hardened usercopy
> 6- powerpc/uaccess: Enable hardened usercopy
> 7- sparc/uaccess: Enable hardened usercopy
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