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

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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>
This commit is contained in:
Jason Gunthorpe 2019-05-22 16:52:52 -03:00
parent 9b1ae605c8
commit 6d7c3cde93
2 changed files with 18 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/hmm.h
View File

@ -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;
};

23
mm/hmm.c
View File

@ -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--;