Messages in this thread | | | Subject | Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data objects | From | Waiman Long <> | Date | Sun, 17 May 2020 22:39:38 -0400 |
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On 5/16/20 8:27 PM, Balbir Singh wrote: > > 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.
We can't disable preemption like that. The vfree() call may potentially sleep. It could be a mess to keep track of the preemption state to make that works.
The purpose of this API is to make sure that a newly allocated memory block won't contain secret left behind from another task. There is no guarantee on how long the freeing process will take.
Cheers, Longman
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