From: Jason Gunthorpe jgg@mellanox.com
[ Upstream commit 6d7c3cde93c1d9ac0b37f78ec3f2ff052159a242 ]
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: Jason Gunthorpe jgg@mellanox.com Reviewed-by: Ira Weiny ira.weiny@intel.com Reviewed-by: John Hubbard jhubbard@nvidia.com Reviewed-by: Ralph Campbell rcampbell@nvidia.com Reviewed-by: Christoph Hellwig hch@lst.de Tested-by: Philip Yang Philip.Yang@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/hmm.h | 1 + mm/hmm.c | 23 +++++++++++++++++------ 2 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/include/linux/hmm.h b/include/linux/hmm.h index 044a36d7c3f8..89508dc0795f 100644 --- a/include/linux/hmm.h +++ b/include/linux/hmm.h @@ -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; }; diff --git a/mm/hmm.c b/mm/hmm.c index f702a3895d05..4c405dfbd2b3 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -104,6 +104,11 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm) 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; @@ -239,9 +249,10 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn, 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--;