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SubjectRe: [PATCH v2] use -fstack-protector-strong
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On Wed, Nov 27, 2013 at 3:27 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Kees Cook <keescook@chromium.org> wrote:
>
>> On a defconfig x86_64 build (with CONFIG_CC_STACKPROTECTOR enabled), the
>> delta in size is just under 9% larger:
>>
>> -rwxrwxr-x 1 kees kees 22134340 Nov 26 10:28 vmlinux.gcc-4.8
>> -rwxrwxr-x 1 kees kees 22123870 Nov 26 10:40 vmlinux.gcc-4.9
>> -rwxrwxr-x 1 kees kees 24225118 Nov 26 10:42 vmlinux.gcc-4.9+strong
>
> Please run it through 'size' so that we know the real text size
> increases.

text data bss dec hex filename
11407474 1453792 1191936 14053202 d66f52 vmlinux.gcc-4.8
11458837 1457504 1191936 14108277 d74675 vmlinux.gcc-4.9
11682929 1457504 1191936 14332369 dab1d1 vmlinux.gcc-4.9+strong

Looks to be 2% for defconfig. That's way better. Shall I send a v3?

> If the cost of -fstack-protector-strong is really +9% in kernel text
> size then that's rather significant!
>
> If this option blows up our performance critical codepaths as well
> then this will likely cause a runtime slowdown as well, in addition to
> the increase in I$ footprint. That needs to be measured.
>
> CONFIG_CC_STACKPROTECTOR=y is relatively cheap today. For example on
> x86-64 defconfig:
>
> text data bss dec filename
> 11378972 1455056 1191936 14025964 vmlinux # CONFIG_CC_STACKPROTECTOR is not set
> 11420243 1455056 1191936 14067235 vmlinux CONFIG_CC_STACKPROTECTOR=y
>
> that's a +0.3% cost currently.

Yeah -- not a lot of functions have char arrays. :)

>
> Thanks,
>
> Ingo

-Kees

--
Kees Cook
Chrome OS Security


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