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

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Date:   Mon, 06 Apr 2020 11:46:26 -0700
From:   Joe Perches <joe@...ches.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Waiman Long <longman@...hat.com>
Cc:     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, 2020-04-06 at 11:06 -0700, Linus Torvalds wrote:
> 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.

Not really as comment and prototype and existing cocci
scripts that contain kzfree are difficult to change.

A sed is straightforward and works well.

$ git grep -w --name-only kzfree | \
  xargs sed -i 's/\bkzfree\b/kfree_sensitive/'

For today's next that's:

$ git diff --shortstat
 116 files changed, 322 insertions(+), 322 deletions(-)

After this change:

The kernel-doc comment in slab_common.c should be
edited from zeroed to something else.

 * kfree_sensitive - like kfree but zero memory
 * @p: object to free memory of
 *
 * The memory of the object @p points to is zeroed before freed.
 * If @p is %NULL, kfree_sensitive() does nothing.
 *
 * Note: this function zeroes the whole allocated buffer which can be a good
 * deal bigger than the requested buffer size passed to kmalloc(). So be
 * careful when using this function in performance sensitive code.
 */