Commit 6d7c3cde authored by Jason Gunthorpe's avatar Jason Gunthorpe
Browse files

mm/hmm: fix use after free with struct hmm in the mmu notifiers 



mmu_notifier_unregister_no_release() is not a fence and the mmu_notifier
system will continue to reference hmm->mn until the srcu grace period
expires.

Resulting in use after free races like this:

         CPU0                                     CPU1
                                               __mmu_notifier_invalidate_range_start()
                                                 srcu_read_lock
                                                 hlist_for_each ()
                                                   // mn == hmm->mn
hmm_mirror_unregister()
  hmm_put()
    hmm_free()
      mmu_notifier_unregister_no_release()
         hlist_del_init_rcu(hmm-mn->list)
			                           mn->ops->invalidate_range_start(mn, range);
					             mm_get_hmm()
      mm->hmm = NULL;
      kfree(hmm)
                                                     mutex_lock(&hmm->lock);

Use SRCU to kfree the hmm memory so that the notifiers can rely on hmm
existing. Get the now-safe hmm struct through container_of and directly
check kref_get_unless_zero to lock it against free.

Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
Reviewed-by: default avatarIra Weiny <ira.weiny@intel.com>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: default avatarRalph Campbell <rcampbell@nvidia.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Tested-by: default avatarPhilip Yang <Philip.Yang@amd.com>
parent 9b1ae605

include/linux/hmm.h

+1 −0
Original line number Diff line number Diff line
@@ -93,6 +93,7 @@ struct hmm { 
	struct mmu_notifier	mmu_notifier;

	struct rw_semaphore	mirrors_sem;

	wait_queue_head_t	wq;

	struct rcu_head		rcu;

	long			notifiers;

	bool			dead;

};

mm/hmm.c

+17 −6
Original line number Diff line number Diff line
@@ -104,6 +104,11 @@ error: 
	return NULL;

}



static void hmm_free_rcu(struct rcu_head *rcu)

{

	kfree(container_of(rcu, struct hmm, rcu));

}



static void hmm_free(struct kref *kref)

{

	struct hmm *hmm = container_of(kref, struct hmm, kref);
@@ -116,7 +121,7 @@ static void hmm_free(struct kref *kref) 
		mm->hmm = NULL;

	spin_unlock(&mm->page_table_lock);



	kfree(hmm);

	mmu_notifier_call_srcu(&hmm->rcu, hmm_free_rcu);

}



static inline void hmm_put(struct hmm *hmm)
@@ -144,10 +149,14 @@ void hmm_mm_destroy(struct mm_struct *mm) 


static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)

{

	struct hmm *hmm = mm_get_hmm(mm);

	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

	struct hmm_mirror *mirror;

	struct hmm_range *range;



	/* Bail out if hmm is in the process of being freed */

	if (!kref_get_unless_zero(&hmm->kref))

		return;



	/* Report this HMM as dying. */

	hmm->dead = true;
@@ -185,13 +194,14 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) 
static int hmm_invalidate_range_start(struct mmu_notifier *mn,

			const struct mmu_notifier_range *nrange)

{

	struct hmm *hmm = mm_get_hmm(nrange->mm);

	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

	struct hmm_mirror *mirror;

	struct hmm_update update;

	struct hmm_range *range;

	int ret = 0;



	VM_BUG_ON(!hmm);

	if (!kref_get_unless_zero(&hmm->kref))

		return 0;



	update.start = nrange->start;

	update.end = nrange->end;
@@ -236,9 +246,10 @@ out: 
static void hmm_invalidate_range_end(struct mmu_notifier *mn,

			const struct mmu_notifier_range *nrange)

{

	struct hmm *hmm = mm_get_hmm(nrange->mm);

	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);



	VM_BUG_ON(!hmm);

	if (!kref_get_unless_zero(&hmm->kref))

		return;



	mutex_lock(&hmm->lock);

	hmm->notifiers--;

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