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

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Message-ID: <c2c8adf48be7cb18bbdf0aef7d21e2defe3d2183.camel@perches.com>
Date:   Mon, 06 Apr 2020 12:38:19 -0700
From:   Joe Perches <joe@...ches.com>
To:     Waiman Long <longman@...hat.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 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.