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

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Message-ID: <CAHmME9rCD1KJNguthAhZ+OAVZTpBwEvGRLRV0tvQjBaEYG1bHQ@mail.gmail.com>
Date:   Tue, 16 Jun 2020 13:46:46 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Joe Perches <joe@...ches.com>
Cc:     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>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        David Sterba <dsterba@...e.cz>, Linux-MM <linux-mm@...ck.org>,
        keyrings@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        linux-pm@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
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        David Miller <davem@...emloft.net>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

On Tue, Jun 16, 2020 at 12:54 PM Joe Perches <joe@...ches.com> 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?

The networking stack has various places where there will be a quick
kmalloc followed by a kfree for an incoming or outgoing packet. One
place that comes to mind would be esp_alloc_tmp, which does a quick
allocation of some temporary kmalloc memory, processes some packet
things inside of that, and then frees it, sometimes in the same
function, and sometimes later in an async callback. I don't know how
"fastpath" you consider this, but usually packet processing is
something people want to do with minimal overhead, considering how
fast NICs are these days.