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

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Message-ID: <20200514120018.GA16070@bombadil.infradead.org>
Date:   Thu, 14 May 2020 05:00:18 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Balbir Singh <bsingharora@...il.com>
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 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.