Linaro-mm-sig May 2024

linaro-mm-sig@lists.linaro.org

27 participants
54 discussions

Re: get_file() unsafe under epoll (was Re: [syzbot] [fs?] [io-uring?] general protection fault in __ep_remove)

by Kees Cook

On Fri, May 03, 2024 at 12:49:11PM -0600, Jens Axboe wrote: > On 5/3/24 12:26 PM, Kees Cook wrote: > > Thanks for doing this analysis! I suspect at least a start of a fix > > would be this: > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > > index 8fe5aa67b167..15e8f74ee0f2 100644 > > --- a/drivers/dma-buf/dma-buf.c > > +++ b/drivers/dma-buf/dma-buf.c > > @@ -267,9 +267,8 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > > > > if (events & EPOLLOUT) { > > /* Paired with fput in dma_buf_poll_cb */ > > - get_file(dmabuf->file); > > - > > - if (!dma_buf_poll_add_cb(resv, true, dcb)) > > + if (!atomic_long_inc_not_zero(&dmabuf->file) && > > + !dma_buf_poll_add_cb(resv, true, dcb)) > > /* No callback queued, wake up any other waiters */ > > Don't think this is sane at all. I'm assuming you meant: > > atomic_long_inc_not_zero(&dmabuf->file->f_count); Oops, yes, sorry. I was typed from memory instead of copy/paste. > but won't fly as you're not under RCU in the first place. And what > protects it from being long gone before you attempt this anyway? This is > sane way to attempt to fix it, it's completely opposite of what sane ref > handling should look like. > > Not sure what the best fix is here, seems like dma-buf should hold an > actual reference to the file upfront rather than just stash a pointer > and then later _hope_ that it can just grab a reference. That seems > pretty horrible, and the real source of the issue. AFAICT, epoll just doesn't hold any references at all. It depends, I think, on eventpoll_release() (really eventpoll_release_file()) synchronizing with epoll_wait() (but I don't see how this happens, and the race seems to be against ep_item_poll() ...?) I'm really confused about how eventpoll manages the lifetime of polled fds. > > Due to this issue I've proposed fixing get_file() to detect pathological states: > > https://lore.kernel.org/lkml/20240502222252.work.690-kees@kernel.org/ > > I don't think this would catch this case, as the memory could just be > garbage at this point. It catches it just fine! :) I tested it against the published PoC. And for cases where further allocations have progressed far enough to corrupt the freed struct file and render the check pointless, nothing different has happened than what happens today. At least now we have a window to catch the situation across the time frame before it is both reallocated _and_ the contents at the f_count offset gets changed to non-zero. -- Kees Cook

2 years, 2 months

Re: [PATCH v3 0/2] drm: Fix dma_resv deadlock at drm object pin time

by Thomas Zimmermann

Hi Am 02.05.24 um 14:00 schrieb Boris Brezillon: > On Thu, 2 May 2024 13:59:41 +0200 > Boris Brezillon <boris.brezillon(a)collabora.com> wrote: > >> Hi Thomas, >> >> On Thu, 2 May 2024 13:51:16 +0200 >> Thomas Zimmermann <tzimmermann(a)suse.de> wrote: >> >>> Hi, >>> >>> ignoring my r-b on patch 1, I'd like to rethink the current patches in >>> general. >>> >>> I think drm_gem_shmem_pin() should become the locked version of _pin(), >>> so that drm_gem_shmem_object_pin() can call it directly. The existing >>> _pin_unlocked() would not be needed any longer. Same for the _unpin() >>> functions. This change would also fix the consistency with the semantics >>> of the shmem _vmap() functions, which never take reservation locks. >>> >>> There are only two external callers of drm_gem_shmem_pin(): the test >>> case and panthor. These assume that drm_gem_shmem_pin() acquires the >>> reservation lock. The test case should likely call drm_gem_pin() >>> instead. That would acquire the reservation lock and the test would >>> validate that shmem's pin helper integrates well into the overall GEM >>> framework. The way panthor uses drm_gem_shmem_pin() looks wrong to me. >>> For now, it could receive a wrapper that takes the lock and that's it. >> I do agree that the current inconsistencies in the naming is >> troublesome (sometimes _unlocked, sometimes _locked, with the version >> without any suffix meaning either _locked or _unlocked depending on >> what the suffixed version does), and that's the very reason I asked >> Dmitry to address that in his shrinker series [1]. So, ideally I'd >> prefer if patches from Dmitry's series were applied instead of >> trying to fix that here (IIRC, we had an ack from Maxime). > With the link this time :-). > > [1]https://lore.kernel.org/lkml/20240105184624.508603-1-dmitry.osipenko@coll… Thanks. I remember these patches. Somehow I thought they would have been merged already. I wasn't super happy about the naming changes in patch 5, because the names of the GEM object callbacks do no longer correspond with their implementations. But anyway. If we go that direction, we should here simply push drm_gem_shmem_pin() and drm_gem_shmem_unpin() into panthor and update the shmem tests with drm_gem_pin(). Panfrost and lima would call drm_gem_shmem_pin_locked(). IMHO we should not promote the use of drm_gem_shmem_object_*() functions, as they are meant to be callbacks for struct drm_gem_object_funcs. (Auto-generating them would be nice.) Best regards Thomas > >> Regards, >> >> Boris -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)

2 years, 2 months

Re: [PATCH v3 0/2] drm: Fix dma_resv deadlock at drm object pin time

by Thomas Zimmermann

Hi, ignoring my r-b on patch 1, I'd like to rethink the current patches in general. I think drm_gem_shmem_pin() should become the locked version of _pin(), so that drm_gem_shmem_object_pin() can call it directly. The existing _pin_unlocked() would not be needed any longer. Same for the _unpin() functions. This change would also fix the consistency with the semantics of the shmem _vmap() functions, which never take reservation locks. There are only two external callers of drm_gem_shmem_pin(): the test case and panthor. These assume that drm_gem_shmem_pin() acquires the reservation lock. The test case should likely call drm_gem_pin() instead. That would acquire the reservation lock and the test would validate that shmem's pin helper integrates well into the overall GEM framework. The way panthor uses drm_gem_shmem_pin() looks wrong to me. For now, it could receive a wrapper that takes the lock and that's it. Best regards Thomas Am 01.05.24 um 08:55 schrieb Adrián Larumbe: > This is v3 of https://lore.kernel.org/dri-devel/20240424090429.57de7d1c@collabora.com/ > > The goal of this patch series is fixing a deadlock upon locking the dma reservation > of a DRM gem object when pinning it, at a prime import operation. > > Changes from v2: > - Removed comment explaining reason why an already-locked > pin function replaced the locked variant inside Panfrost's > object pin callback. > - Moved already-assigned attachment warning into generic > already-locked gem object pin function > > Adrián Larumbe (2): > drm/panfrost: Fix dma_resv deadlock at drm object pin time > drm/gem-shmem: Add import attachment warning to locked pin function > > drivers/gpu/drm/drm_gem_shmem_helper.c | 2 ++ > drivers/gpu/drm/lima/lima_gem.c | 2 +- > drivers/gpu/drm/panfrost/panfrost_gem.c | 2 +- > 3 files changed, 4 insertions(+), 2 deletions(-) > > > base-commit: 75b68f22e39aafb22f3d8e3071e1aba73560788c -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)

2 years, 2 months

Re: [PATCH v3 1/2] drm/panfrost: Fix dma_resv deadlock at drm object pin time

by Thomas Zimmermann

Hi Am 01.05.24 um 08:55 schrieb Adrián Larumbe: > When Panfrost must pin an object that is being prepared a dma-buf > attachment for on behalf of another driver, the core drm gem object pinning > code already takes a lock on the object's dma reservation. > > However, Panfrost GEM object's pinning callback would eventually try taking > the lock on the same dma reservation when delegating pinning of the object > onto the shmem subsystem, which led to a deadlock. > > This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws > the following recursive locking situation: > > weston/3440 is trying to acquire lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_pin+0x34/0xb8 [drm_shmem_helper] > but task is already holding lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pin+0x2c/0x80 [drm] > > Fix it by assuming the object's reservation had already been locked by the > time we reach panfrost_gem_pin. Maybe say that the reservation lock has been taken in drm_gem_pin() > > Do the same thing for the Lima driver, as it most likely suffers from the > same issue. Please split this patch into one for panfrost and one for lima. To each patch, you can add Reviewed-by: Thomas Zimmermann <tzimmermann(a)suse.de> Best regards Thomas > > Cc: Thomas Zimmermann <tzimmermann(a)suse.de> > Cc: Dmitry Osipenko <dmitry.osipenko(a)collabora.com> > Cc: Boris Brezillon <boris.brezillon(a)collabora.com> > Cc: Steven Price <steven.price(a)arm.com> > Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()") > Signed-off-by: Adrián Larumbe <adrian.larumbe(a)collabora.com> > --- > drivers/gpu/drm/lima/lima_gem.c | 2 +- > drivers/gpu/drm/panfrost/panfrost_gem.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c > index 7ea244d876ca..c4e0f9faaa47 100644 > --- a/drivers/gpu/drm/lima/lima_gem.c > +++ b/drivers/gpu/drm/lima/lima_gem.c > @@ -185,7 +185,7 @@ static int lima_gem_pin(struct drm_gem_object *obj) > if (bo->heap_size) > return -EINVAL; > > - return drm_gem_shmem_pin(&bo->base); > + return drm_gem_shmem_object_pin(obj); > } > > static int lima_gem_vmap(struct drm_gem_object *obj, struct iosys_map *map) > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c > index d47b40b82b0b..f268bd5c2884 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_gem.c > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c > @@ -192,7 +192,7 @@ static int panfrost_gem_pin(struct drm_gem_object *obj) > if (bo->is_heap) > return -EINVAL; > > - return drm_gem_shmem_pin(&bo->base); > + return drm_gem_shmem_object_pin(obj); > } > > static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj) -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)

2 years, 2 months

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