[PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()
mhocko at kernel.org
Wed Jun 17 09:12:12 CEST 2020
On Tue 16-06-20 17:37:11, Matthew Wilcox wrote:
> On Wed, Jun 17, 2020 at 01:01:30AM +0200, David Sterba wrote:
> > On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote:
> > > On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:
> > > > v4:
> > > > - Break out the memzero_explicit() change as suggested by Dan Carpenter
> > > > so that it can be backported to stable.
> > > > - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for
> > > > now as there can be a bit more discussion on what is best. It will be
> > > > introduced as a separate patch later on after this one is merged.
> > >
> > > To this larger audience and last week without reply:
> > > https://firstname.lastname@example.org/
> > >
> > > Are there _any_ fastpath uses of kfree or vfree?
> > I'd consider kfree performance critical for cases where it is called
> > under locks. If possible the kfree is moved outside of the critical
> > section, but we have rbtrees or lists that get deleted under locks and
> > restructuring the code to do eg. splice and free it outside of the lock
> > is not always possible.
> Not just performance critical, but correctness critical. Since kvfree()
> may allocate from the vmalloc allocator, I really think that kvfree()
> should assert that it's !in_atomic(). Otherwise we can get into trouble
> if we end up calling vfree() and have to take the mutex.
FWIW __vfree already checks for atomic context and put the work into a
deferred context. So this should be safe. It should be used as a last
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