linux-kernel - Re: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers

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] [day] [month] [year] [list]

Message-ID: <20210915191023.GF4323@worktop.programming.kicks-ass.net>
Date:   Wed, 15 Sep 2021 21:10:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Jann Horn <jannh@...gle.com>, Peter Oskolkov <posk@...gle.com>,
        Peter Oskolkov <posk@...k.io>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Andrei Vagin <avagin@...gle.com>,
        Thierry Delisle <tdelisle@...terloo.ca>
Subject: Re: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers

On Wed, Sep 15, 2021 at 09:50:41AM -0700, Andy Lutomirski wrote:
> What's the precise problem?  The code would be roughly:
> 
> if (try_pin_the_page) {
>   write it;
>   unpin;
> } else {
>   do nothing -- .fault will fill in the correct contents.
> }
> 
> The time this takes is nondeterministic, but it's bounded and short.

You can't do this from sched_submit_work(), you might already hold
mmap_sem. Hence the suggestion to, for UMCG registered threads, pin the
page(s) on syscall-enter and unpin on either schedule() or
syscall-return.