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Date: Fri, 22 Jan 2016 11:57:05 -0800
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <laura@...bott.name>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Ingo Molnar <mingo@...hat.com>,
Andy Lutomirski <luto@...capital.net>, "H. Peter Anvin" <hpa@...or.com>,
Michael Ellerman <mpe@...erman.id.au>, Mathias Krause <minipli@...glemail.com>,
Thomas Gleixner <tglx@...utronix.de>, "x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
PaX Team <pageexec@...email.hu>, Emese Revfy <re.emese@...il.com>,
LKML <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v4 0/8] introduce post-init read-only memory
On Fri, Jan 22, 2016 at 11:16 AM, Laura Abbott <laura@...bott.name> wrote:
> On 1/22/16 9:19 AM, David Brown wrote:
>>
>> On Tue, Jan 19, 2016 at 10:08:34AM -0800, Kees Cook wrote:
>>
>>> This introduces __ro_after_init as a way to mark such memory, and uses
>>> it on the x86 vDSO to kill an extant kernel exploitation method. Also
>>> adds a new kernel parameter to help debug future use and adds an lkdtm
>>> test to check the results.
>>
>>
>> I've tested these patches on 32-bit ARM using the provoke-crashes
>> test. However, they do require CONFIG_ARM_KERNMEM_PERMS to be enabled
>> as well, which does incur additional memory usage.
Thanks for testing!
>> Do we want to consider making CONFIG_ARM_KERNMEM_PERMS default y for
>> security reasons, and just document that memory-constrained systems
>> may want to turn it off?
>>
>> I'll test the arm64 next.
>>
>> David
>
>
> Kees had previously pushed a patch to do so but it exposed a couple of
> underlying issues, mostly with low power paths
> (c.f. http://article.gmane.org/gmane.linux.ports.arm.kernel/471199,
> http://article.gmane.org/gmane.linux.kernel.mm/143489)
> Those will need to be all fixed up before this could be made default.
Yeah, I've got a patch waiting to reorganize CONFIG_ARM_KERNMEM_PERMS
to look more like arm64 (and x86) and get the feature correctly under
CONFIG_DEBUG_RODATA. I made it default=y on v7+. rmk asked me to wait
until -rc1 before resubmitting it.
http://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/commit/?h=kspp/arm-rodata&id=08bebfd2e7fb8a9f364ced74c356642d64e1f43e
and a small improvement too:
http://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/commit/?h=kspp/arm-rodata&id=8e16f005ce0d4069aee5502379cff845b4c6f950
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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