linux-kernel - Re: [kernel-hardening] [PATCH v4 0/8] introduce post-init read-only memory

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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: [kernel-hardening] [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