linux-kernel - Re: [PATCH v2 1/4] mm: correct mask size for slub page->objects

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: <20190912094035.vkqnj24bwh33yvia@box>
Date:   Thu, 12 Sep 2019 12:40:35 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] mm: correct mask size for slub page->objects

On Wed, Sep 11, 2019 at 08:31:08PM -0600, Yu Zhao wrote:
> Mask of slub objects per page shouldn't be larger than what
> page->objects can hold.
> 
> It requires more than 2^15 objects to hit the problem, and I don't
> think anybody would. It'd be nice to have the mask fixed, but not
> really worth cc'ing the stable.
> 
> Fixes: 50d5c41cd151 ("slub: Do not use frozen page flag but a bit in the page counters")
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>

I don't think the patch fixes anything.

Yes, we have one spare bit between order and number of object that is not
used and always zero. So what?

I can imagine for some microarchitecures accessing higher 16 bits of int
is cheaper than shifting by 15.

-- 
 Kirill A. Shutemov