linux-kernel - Re: [PATCH] mm: Add kvfree_sensitive() for freeing sensitive data objects

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Message-ID: <CAHk-=wgjiHUWLZWKZJ4eU+RrOc2xNZCHn4ETmJ0S+H=Eig28Cw@mail.gmail.com>
Date:   Mon, 6 Apr 2020 11:06:02 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Joe Perches <joe@...ches.com>, David Howells <dhowells@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linux-MM <linux-mm@...ck.org>, keyrings@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Add kvfree_sensitive() for freeing sensitive data objects

On Mon, Apr 6, 2020 at 10:59 AM Waiman Long <longman@...hat.com> wrote:
>
> I have actually been thinking about that. I saw a couple of cases in the
> crypto code where a memzero_explicit() is followed by kfree(). Those can
> be replaced by kfree_sensitive.

Ack.

Doing that (and renaming kvzfree) should be a fairly straightforward
coccinelle patch.

Somebody (maybe you) asked whether we could just use
kvfree_sensitive() for everything, We probably could. The extra test
is cheap - much cheaper than the memzero_explicit().

That said, _there_ I think that consistency with regular kfree/kvfree
naming means that we might as well keep separate names, and keep the
kmalloc->kfree_sensitive and kvmalloc->kvfree_sensitive pairing. Even
if technically we could do with just the one function that works for
both cases.

            Linus