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Message-ID: <CAKv+Gu_AiynfdBVvm6fbFX8sRi7ZwWGFGG9rUhoVCP0Bc-EaZg@mail.gmail.com>
Date: Thu, 3 Aug 2017 19:27:25 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Kees Cook <keescook@...omium.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 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.
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