linux-kernel - Re: [PATCH v2] random: set fast pool count to zero in cpuhp teardown

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 for Android: free password hash cracker in your pocket

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

Date:   Mon, 14 Feb 2022 15:52:34 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v2] random: set fast pool count to zero in cpuhp teardown

On Mon, Feb 14, 2022 at 3:49 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2022-02-14 15:42:50 [+0100], Jason A. Donenfeld wrote:
> > Hi Sebastian,
> Hi Jason,
>
> > If we move this to startup, is there a phase during which no interrupt
> > will arrive? That is, can this happen very very early in startup, so
> > that zeroing out count happens *before* ++count?
>
> Interrupts will arrive starting with CPUHP_AP_ONLINE_IDLE from the CPU
> HP point of view. My suggestion had a check for upper most bit and only
> clear count if that bit was seen. So we wouldn't clear the counter if we
> wouldn't suspect one of the rare corner cases.

That doesn't work for the other use cases I have for this (see the other patch).

So I think it seems better to keep it before CPUHP_TIMERS_PREPARE, but
do it on startup rather than teardown. Seem reasonable? Would that
mean we zero out before IRQs are enabled?