linux-kernel - Re: [PATCH v2] mm: Add kvfree_sensitive() for freeing sensitive data objects

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Message-ID: <1e4a6174-04be-6c05-fd6e-b43fefd317fc@redhat.com>
Date:   Mon, 6 Apr 2020 22:16:04 -0400
From:   Waiman Long <longman@...hat.com>
To:     Joe Perches <joe@...ches.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>
Cc:     linux-mm@...ck.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2] mm: Add kvfree_sensitive() for freeing sensitive data
 objects

On 4/6/20 3:38 PM, Joe Perches wrote:
> On Mon, 2020-04-06 at 14:58 -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.
> [] 
>>  extern void kvfree(const void *addr);
>> +extern void kvfree_sensitive(const void *addr, size_t len);
> Question: why should this be const?
>
> 2.1.44 changed kfree(void *) to kfree(const void *) but
> I didn't find a particular reason why.

I am just following the function prototype used by kvfree(). Even
kzfree(const void *) use const. I can remove "const" if others agree.

Cheers,
Longman