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Date: Thu, 7 Jul 2016 13:27:03 -0400
From: Kees Cook <>
To: Christian Borntraeger <>
Cc: LKML <>, Rik van Riel <>, 
	Casey Schaufler <>, PaX Team <>, 
	Brad Spengler <>, Russell King <>, 
	Catalin Marinas <>, Will Deacon <>, 
	Ard Biesheuvel <>, 
	Benjamin Herrenschmidt <>, Michael Ellerman <>, 
	Tony Luck <>, Fenghua Yu <>, 
	"David S. Miller" <>, "" <>, Christoph Lameter <>, 
	Pekka Enberg <>, David Rientjes <>, 
	Joonsoo Kim <>, Andrew Morton <>, 
	Andy Lutomirski <>, Mathias Krause <>, Jan Kara <>, 
	Vitaly Wool <>, Andrea Arcangeli <>, 
	Dmitry Vyukov <>, Laura Abbott <>, 
	"" <>,, 
	"" <>, sparclinux <>, 
	linux-arch <>, Linux-MM <>, 
	"" <>
Subject: Re: [PATCH 0/9] mm: Hardened usercopy

On Thu, Jul 7, 2016 at 3:30 AM, Christian Borntraeger
<> wrote:
> 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
>> 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
> Was there a reason why you did not change s390?

No reason -- just didn't have a good build setup for testing it.
(Everything but arm64 was already in grsecurity, and I was able to
build-test arm64 when I added it there.) I would love to include s390


Kees Cook
Chrome OS & Brillo Security

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