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

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Date:   Sun, 3 May 2020 22:57:23 -0400
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Eric Biggers <ebiggers@...nel.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 5/1/20 7:22 PM, Eric Biggers wrote:
> 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
>
Andrew, would you mind taking this patch into the mm-tree?

Thanks,
Longman