linux-kernel - Re: [PATCH] lib/strscpy: remove word-at-a-time optimization.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+55aFwqDxBSKf3u2Uv-90vrhx4WSoQunOPU3witzCAuNhYBhg@mail.gmail.com>
Date:   Thu, 25 Jan 2018 09:55:00 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Eryu Guan <eguan@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Chris Metcalf <metcalf@...m.mit.edu>,
        David Laight <David.Laight@...lab.com>,
        stable <stable@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] lib/strscpy: remove word-at-a-time optimization.

On Thu, Jan 25, 2018 at 12:32 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Wed, Jan 24, 2018 at 6:52 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> So I'd *much* rather have some way to tell KASAN that word-at-a-time
>> is going on. Because that approach definitely makes a difference in
>> other places.
>
> The other option was to use READ_ONCE_NOCHECK().

How about just using the same accessor that we do for the dcache case.
That gives a reasonable example of the whole word-at-a-time model, and
should be good.

COMPLETELY UNTESTED patch attached. This needs to be verified.

It does limit the word-at-a-time code to the architectures that select
both HAVE_EFFICIENT_UNALIGNED_ACCESS and DCACHE_WORD_ACCESS, but that
seems a reasonable choice anyway.

               Linus

View attachment "patch.diff" of type "text/plain" (1651 bytes)