From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: [PATCH v4 0/1] Use HMM for ODP v4 Date: Wed, 22 May 2019 18:04:20 -0400 Message-ID: <20190522220419.GB20179@redhat.com> References: <20190411181314.19465-1-jglisse@redhat.com> <20190506195657.GA30261@ziepe.ca> <20190521205321.GC3331@redhat.com> <20190522005225.GA30819@ziepe.ca> <20190522174852.GA23038@redhat.com> <20190522201247.GH6054@ziepe.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190522201247.GH6054@ziepe.ca> Sender: linux-kernel-owner@vger.kernel.org To: Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, Leon Romanovsky , Doug Ledford , Artemy Kovalyov , Moni Shoua , Mike Marciniszyn , Kaike Wan , Dennis Dalessandro List-Id: linux-rdma@vger.kernel.org On Wed, May 22, 2019 at 05:12:47PM -0300, Jason Gunthorpe wrote: > On Wed, May 22, 2019 at 01:48:52PM -0400, Jerome Glisse wrote: > > > static void put_per_mm(struct ib_umem_odp *umem_odp) > > { > > struct ib_ucontext_per_mm *per_mm = umem_odp->per_mm; > > @@ -325,9 +283,10 @@ static void put_per_mm(struct ib_umem_odp *umem_odp) > > up_write(&per_mm->umem_rwsem); > > > > WARN_ON(!RB_EMPTY_ROOT(&per_mm->umem_tree.rb_root)); > > - mmu_notifier_unregister_no_release(&per_mm->mn, per_mm->mm); > > + hmm_mirror_unregister(&per_mm->mirror); > > put_pid(per_mm->tgid); > > - mmu_notifier_call_srcu(&per_mm->rcu, free_per_mm); > > + > > + kfree(per_mm); > > Notice that mmu_notifier only uses SRCU to fence in-progress ops > callbacks, so I think hmm internally has the bug that this ODP > approach prevents. > > hmm should follow the same pattern ODP has and 'kfree_srcu' the hmm > struct, use container_of in the mmu_notifier callbacks, and use the > otherwise vestigal kref_get_unless_zero() to bail: > > From 0cb536dc0150ba964a1d655151d7b7a84d0f915a Mon Sep 17 00:00:00 2001 > From: Jason Gunthorpe > Date: Wed, 22 May 2019 16:52:52 -0300 > Subject: [PATCH] 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. > > 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. It is already badly handled with BUG_ON(), i just need to convert those to return and to use mmu_notifier_call_srcu() to free hmm struct. The way race is avoided is because mm->hmm will either be NULL or point to another hmm struct before an existing hmm is free. Also if range_start/range_end use kref_get_unless_zero() but right now this is BUG_ON if it turn out to be NULL, it should just return on NULL. > > Signed-off-by: Jason Gunthorpe > --- > include/linux/hmm.h | 1 + > mm/hmm.c | 25 +++++++++++++++++++------ > 2 files changed, 20 insertions(+), 6 deletions(-) > > diff --git a/include/linux/hmm.h b/include/linux/hmm.h > index 51ec27a8466816..8b91c90d3b88cb 100644 > --- a/include/linux/hmm.h > +++ b/include/linux/hmm.h > @@ -102,6 +102,7 @@ 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 816c2356f2449f..824e7e160d8167 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -113,6 +113,11 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm) > return NULL; > } > > +static void hmm_fee_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); > @@ -125,7 +130,7 @@ 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_fee_rcu); > } > > static inline void hmm_put(struct hmm *hmm) > @@ -153,10 +158,14 @@ 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; > > + /* hmm is in progress to free */ > + if (!kref_get_unless_zero(&hmm->kref)) > + return; > + > /* Report this HMM as dying. */ > hmm->dead = true; > > @@ -194,13 +203,15 @@ 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); > + /* hmm is in progress to free */ > + if (!kref_get_unless_zero(&hmm->kref)) > + return 0; > > update.start = nrange->start; > update.end = nrange->end; > @@ -248,9 +259,11 @@ 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); > + /* hmm is in progress to free */ > + if (!kref_get_unless_zero(&hmm->kref)) > + return; > > mutex_lock(&hmm->lock); > hmm->notifiers--; > -- > 2.21.0 >