linux-kernel - Re: [PATCH] random: use correct memory barriers for crng_node

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: <20200921235136.GA6796@gondor.apana.org.au>
Date:   Tue, 22 Sep 2020 09:51:36 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Eric Biggers <ebiggers@...nel.org>, tytso@....edu,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] random: use correct memory barriers for crng_node_pool

On Mon, Sep 21, 2020 at 04:26:39PM -0700, Paul E. McKenney wrote:
>
> > But this reasoning could apply to any data structure that contains
> > a spin lock, in particular ones that are dereferenced through RCU.
> 
> I lost you on this one.  What is special about a spin lock?

I don't know, that was Eric's concern.  He is inferring that
spin locks through lockdep debugging may trigger dependencies
that require smp_load_acquire.

Anyway, my point is if it applies to crng_node_pool then it
would equally apply to RCU in general.

> > So my question if this reasoning is valid, then why aren't we first
> > converting rcu_dereference to use smp_load_acquire?
> 
> For LTO in ARM, rumor has it that Will is doing so.  Which was what
> motivated the BoF on this topic at Linux Plumbers Conference.

Sure, if RCU switches over to smp_load_acquire then I would have
no problems with everybody else following in its footsteps.

Here is the original patch in question:

https://lore.kernel.org/lkml/20200916233042.51634-1-ebiggers@kernel.org/

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt