linux-kernel - Re: [PATCH v2 0/3] Fix some incompatibilites between KASAN and FORTIFY

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Message-ID: <87o8tkrjud.fsf@dja-thinkpad.axtens.net>
Date:   Thu, 27 Feb 2020 10:48:26 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com
Cc:     linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, x86@...nel.org, dvyukov@...gle.com,
        christophe.leroy@....fr
Subject: Re: [PATCH v2 0/3] Fix some incompatibilites between KASAN and FORTIFY_SOURCE

Daniel Axtens <dja@...ens.net> writes:

> 3 KASAN self-tests fail on a kernel with both KASAN and FORTIFY_SOURCE:
> memchr, memcmp and strlen. I have observed this on x86 and powerpc.
>
> When FORTIFY_SOURCE is on, a number of functions are replaced with
> fortified versions, which attempt to check the sizes of the
> operands. However, these functions often directly invoke __builtin_foo()
> once they have performed the fortify check.
>
> This breaks things in 2 ways:
>
>  - the three function calls are technically dead code, and can be
>    eliminated. When __builtin_ versions are used, the compiler can detect
>    this.
>
>  - Using __builtins may bypass KASAN checks if the compiler decides to
>    inline it's own implementation as sequence of instructions, rather than
>    emit a function call that goes out to a KASAN-instrumented
>    implementation.
>
> The patches address each reason in turn. Finally, test_memcmp used a
> stack array without explicit initialisation, which can sometimes break
> too, so fix that up.

Hi all,

It doesn't look like this has been picked up yet. Is there anything I
can do to help things along?

Regards,
Daniel

>
> v2: - some cleanups, don't mess with arch code as I missed some wrinkles.
>     - add stack array init (patch 3)
>
> Daniel Axtens (3):
>   kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE
>   string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
>   kasan: initialise array in kasan_memcmp test
>
>  include/linux/string.h | 60 +++++++++++++++++++++++++++++++++---------
>  lib/test_kasan.c       | 32 +++++++++++++---------
>  2 files changed, 68 insertions(+), 24 deletions(-)
>
> -- 
> 2.20.1