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

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Message-ID: <f779dea1-3b50-e354-3914-7394b4473f5b@gmail.com>
Date:   Sun, 17 May 2020 10:27:39 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     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>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data
 objects



On 14/5/20 10:00 pm, Matthew Wilcox wrote:
> On Thu, May 14, 2020 at 09:00:40PM +1000, Balbir Singh wrote:
>> I wonder if the right thing to do is also to disable pre-emption, just so that the thread does not linger on with sensitive data.
>>
>> void kvfree_sensitive(const void *addr, size_t len)
>> {
>> 	preempt_disable();
>> 	if (likely(!ZERO_OR_NULL_PTR(addr))) {
>> 		memzero_explicit((void *)addr, len);
>> 		kvfree(addr);
>> 	}
>> 	preempt_enable();
>> }
>> EXPORT_SYMBOL(kvfree_sensitive);
> 
> If it's _that_ sensitive then the caller should have disabled preemption.
> Because preemption could otherwise have occurred immediately before
> kvfree_sensitive() was called.
> 

May be, but the callers of the API have to be explictly aware of the contract.
I don't disagree with you on what you've said, but I was referring to the
intent of freeing sensitive data vs the turn around time for doing so.

Balbir Singh.