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From:   David Howells <dhowells@redhat.com>
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To:     Linus Torvalds <torvalds@linux-foundation.org>
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        Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        James Morris <jmorris@namei.org>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v2] mm: Add kvfree_sensitive() for freeing sensitive data objects
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Date:   Tue, 07 Apr 2020 22:14:11 +0100
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Linus Torvalds <torvalds@linux-foundation.org> wrote:

> So the _real_ prototype for 'free()'-like operations should be something=
 like
> =

>     void free(const volatile killed void *ptr);
> =

> where that "killed" also tells the compiler that the pointer lifetime
> is dead, so that using it afterwards is invalid. So that the compiler
> could warn us about some of the most trivial use-after-free cases.

It might be worth asking the compiler folks to give us an __attribute__ fo=
r
that - even if they don't do anything with it immediately.  So we might ha=
ve
something like:

	void free(const volatile void *ptr) __attribute__((free(1)));

There are some for allocation functions, some of which we use, though I'm =
not
sure we do so as consistently as we should (should inline functions like
kcalloc() have them, for example?).

David