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Date:   Sun, 17 May 2020 10:27:39 +1000
From:   Balbir Singh <>
To:     Matthew Wilcox <>
Cc:     Waiman Long <>,
        Andrew Morton <>,
        David Howells <>,
        Jarkko Sakkinen <>,
        James Morris <>,
        "Serge E. Hallyn" <>,,,,
        Linus Torvalds <>,
        Joe Perches <>,
        David Rientjes <>
Subject: Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data

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.

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