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Date: Thu, 3 Aug 2017 15:14:45 -0700
From: Kees Cook <keescook@...omium.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>, Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC/RFT PATCH] gcc-plugins: force initialize auto variables
whose addresses are taken
On Thu, Aug 3, 2017 at 11:27 AM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> On 3 August 2017 at 05:35, Kees Cook <keescook@...omium.org> wrote:
>> On Thu, Jul 6, 2017 at 4:16 PM, Kees Cook <keescook@...omium.org> wrote:
>>> On Thu, Jul 6, 2017 at 2:44 PM, Kees Cook <keescook@...omium.org> wrote:
>>>> On Thu, Jul 6, 2017 at 4:09 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>>>> On Thu, Jul 6, 2017 at 12:13 PM, Ard Biesheuvel
>>>>> <ard.biesheuvel@...aro.org> wrote:
>>>>>> To prevent leaking stack contents in cases where it is not possible
>>>>>> for the compiler to figure out whether an automatic variable has been
>>>>>> initialized or not, add a plugin that forcibly initializes all automatic
>>>>>> variables of struct/union types if their address is taken at any point.
>>>>>>
>>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>>>>
>>>> Ard, I'd be curious what you see for "size" difference between builds
>>>> and if it's visible with hackbench or other things?
>>>
>>> Hm, not all that bad on the size front:
>>>
>>> text data bss dec
>>> hex filename
>>> 10950705 5592525 13955072 30498302 1d15dfe vmlinux
>>> 11048035 5592365 13955072 30595472 1d2d990
>>> vmlinux.initautobyref
>>>
>>> And yes, as expected, wow there are a lot of notices in verbose mode. ;)
>>>
>>> My pet favorite, from the NAKed patch I sent forever ago, is covered
>>> (as expected):
>>>
>>> net/socket.c: In function ‘SYSC_getsockname’:
>>> net/socket.c:1605:26: note: auto variable will be forcibly initialized
>>> struct sockaddr_storage address;
>>> ^~~~~~~
>>
>> While this was an RFC, it seems to work well and, as Daniel mentioned,
>> provides another benchmark for future optimizations of this kind of
>> protection. Besides the COMPILE_TEST change already discussed, any
>> other changes or objections before I carry this in -next?
>>
>
> Sounds reasonable to me.
Actually, I just looked at the diff between structleak and
initautobyref, and it's essentially 1 test (and the removal of all the
__user-detection code):
- /* if the type is of interest, examine the variable */
- if (TYPE_USERSPACE(type))
+ /* initialize the variable if its address is taken */
+ if (TREE_ADDRESSABLE (var))
Perhaps instead of a whole new plugin, could we just add the
functionality to the existing structleak plugin as a Kconfig option?
Like maybe CONFIG_GCC_PLUGIN_STRUCTLEAK_TAKEN?
-Kees
--
Kees Cook
Pixel Security
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