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Subject: Re: [PATCH v2] mm: Add kvfree_sensitive() for freeing sensitive data
 objects
To:     Joe Perches <joe@perches.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Howells <dhowells@redhat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>
Cc:     linux-mm@kvack.org, keyrings@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        David Rientjes <rientjes@google.com>
References: <20200406185827.22249-1-longman@redhat.com>
 <c2c8adf48be7cb18bbdf0aef7d21e2defe3d2183.camel@perches.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <1e4a6174-04be-6c05-fd6e-b43fefd317fc@redhat.com>
Date:   Mon, 6 Apr 2020 22:16:04 -0400
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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