linux-kernel - Re: [PATCH 12/12] locking/rwsem: Make MSbit of count as guard bit to fail readlock

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: <4e923bea-0e3b-ba50-c45c-f7b281a29176@redhat.com>
Date:   Thu, 28 Mar 2019 16:55:34 -0400
From:   Waiman Long <longman@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH 12/12] locking/rwsem: Make MSbit of count as guard bit to
 fail readlock

On 03/28/2019 04:47 PM, Linus Torvalds wrote:
> On Thu, Mar 28, 2019 at 11:12 AM Waiman Long <longman@...hat.com> wrote:
>> With the merging of owner into count for x86-64, there is only 16 bits
>> left for reader count. It is theoretically possible for an application to
>> cause more than 64k readers to acquire a rwsem leading to count overflow.
> Ahh, and here's the thing that makes 16 bits work for readers.
>
> I think this at a minimum needs to be made very clear in the patch
> that actually lowered the reader count bits, but preferably this just
> needs to be done *before* that patch, so that you don't have a point
> in history where rwlocks are simply not reliable.
>
>                Linus

Thanks for the suggestion. I will move this patch up in the next version.

Cheers,
Longman