linux-kernel - Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data objects

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Date:   Fri, 1 May 2020 16:22:24 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     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>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data
 objects

On Tue, Apr 07, 2020 at 04:03:18PM -0400, Waiman Long wrote:
> For kvmalloc'ed data object that contains sensitive information like
> cryptographic key, we need to make sure that the buffer is always
> cleared before freeing it. Using memset() alone for buffer clearing may
> not provide certainty as the compiler may compile it away. To be sure,
> the special memzero_explicit() has to be used.
> 
> This patch introduces a new kvfree_sensitive() for freeing those
> sensitive data objects allocated by kvmalloc(). The relevnat places
> where kvfree_sensitive() can be used are modified to use it.
> 
> Fixes: 4f0882491a14 ("KEYS: Avoid false positive ENOMEM error on key read")
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Waiman Long <longman@...hat.com>

Looks good, feel free to add:

Reviewed-by: Eric Biggers <ebiggers@...gle.com>

(I don't really buy the argument that the compiler could compile away memset()
before kvfree().  But I agree with using memzero_explicit() anyway to make the
intent explicit.)

I don't see this patch in linux-next yet.  Who is planning to take this patch?
Presumably David through the keyrings tree, or Andrew through mm?

- Eric