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Date:   Wed, 8 Nov 2017 17:12:31 -0800
From:   Kees Cook <>
To:     Laura Abbott <>
Cc:     Andrew Morton <>,
        Masahiro Yamada <>,
        Arnd Bergmann <>,
        Josh Triplett <>,
        Nicholas Piggin <>,
        linux-kbuild <>,
        LKML <>
Subject: Re: [PATCH v2 0/3] Makefile: Introduce CONFIG_CC_STACKPROTECTOR_AUTO

On Wed, Nov 8, 2017 at 11:43 AM, Laura Abbott <> wrote:
> On 11/07/2017 09:38 AM, Kees Cook wrote:
>> As described in the final patch:
>> Nearly all modern compilers support a stack-protector option, and nearly
>> all modern distributions enable the kernel stack-protector, so enabling
>> this by default in kernel builds would make sense. However, Kconfig does
>> not have knowledge of available compiler features, so it isn't safe to
>> force on, as this would unconditionally break builds for the compilers
>> or architectures that don't have support. Instead, this introduces a new
>> option, CONFIG_CC_STACKPROTECTOR_AUTO, which attempts to discover the best
>> possible stack-protector available, and will allow builds to proceed even
>> if the compiler doesn't support any stack-protector.
>> This option is made the default so that kernels built with modern
>> compilers will be protected-by-default against stack buffer overflows,
>> avoiding things like the recent BlueBorne attack. Selection of a specific
>> stack-protector option remains available, including disabling it.
>> This has lived over the last several days without any unfixed 0day
>> failures.
>> v2:
>> - under ..._AUTO, warn and continue on _all_ stack protector failure cases
>> - fix 32-bit boot regression due to lazy gz.
>> - set CONFIG_CC_STACKPROTECTOR_NONE for tiny.config.
>> Thanks,
>> -Kees
> This passed a test build on all Fedora arches, including s390 and ppc.
> On x86 it picks up the strong option correctly.
> You're welcome to add
> Tested-by: Laura Abbott <>

Awesome, thanks for testing!


Kees Cook
Pixel Security

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