netdev - Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree

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Message-ID: <20200617003711.GD8681@bombadil.infradead.org>
Date:   Tue, 16 Jun 2020 17:37:11 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     dsterba@...e.cz, Joe Perches <joe@...ches.com>,
        Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Jason A . Donenfeld" <Jason@...c4.com>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-amlogic@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-ppp@...r.kernel.org, wireguard@...ts.zx2c4.com,
        linux-wireless@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
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        linux-nfs@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org
Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

On Wed, Jun 17, 2020 at 01:01:30AM +0200, David Sterba wrote:
> On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote:
> > On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:
> > >  v4:
> > >   - Break out the memzero_explicit() change as suggested by Dan Carpenter
> > >     so that it can be backported to stable.
> > >   - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for
> > >     now as there can be a bit more discussion on what is best. It will be
> > >     introduced as a separate patch later on after this one is merged.
> > 
> > To this larger audience and last week without reply:
> > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
> > 
> > Are there _any_ fastpath uses of kfree or vfree?
> 
> I'd consider kfree performance critical for cases where it is called
> under locks. If possible the kfree is moved outside of the critical
> section, but we have rbtrees or lists that get deleted under locks and
> restructuring the code to do eg. splice and free it outside of the lock
> is not always possible.

Not just performance critical, but correctness critical.  Since kvfree()
may allocate from the vmalloc allocator, I really think that kvfree()
should assert that it's !in_atomic().  Otherwise we can get into trouble
if we end up calling vfree() and have to take the mutex.