[PATCH] dma-resv: Fix dma_resv_get_fences and dma_resv_copy_fences after conversion
Christian König
christian.koenig at amd.com
Fri Oct 8 10:21:23 UTC 2021
Am 08.10.21 um 11:50 schrieb Tvrtko Ursulin:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>
> Cache the count of shared fences in the iterator to avoid dereferencing
> the dma_resv_object outside the RCU protection. Otherwise iterator and its
> users can observe an incosistent state which makes it impossible to use
> safely.
Ah, of course! I've been staring at the code the whole morning and
couldn't see it.
Going to write a testcase to cover that.
> Such as:
>
> <6> [187.517041] [IGT] gem_sync: executing
> <7> [187.536343] i915 0000:00:02.0: [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
> <7> [187.536793] i915 0000:00:02.0: [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
> <6> [187.551235] [IGT] gem_sync: starting subtest basic-many-each
> <1> [188.935462] BUG: kernel NULL pointer dereference, address: 0000000000000010
> <1> [188.935485] #PF: supervisor write access in kernel mode
> <1> [188.935495] #PF: error_code(0x0002) - not-present page
> <6> [188.935504] PGD 0 P4D 0
> <4> [188.935512] Oops: 0002 [#1] PREEMPT SMP NOPTI
> <4> [188.935521] CPU: 2 PID: 1467 Comm: gem_sync Not tainted 5.15.0-rc4-CI-Patchwork_21264+ #1
> <4> [188.935535] Hardware name: /NUC6CAYB, BIOS AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
> <4> [188.935546] RIP: 0010:dma_resv_get_fences+0x116/0x2d0
> <4> [188.935560] Code: 10 85 c0 7f c9 be 03 00 00 00 e8 15 8b df ff eb bd e8 8e c6 ff ff eb b6 41 8b 04 24 49 8b 55 00 48 89 e7 8d 48 01 41 89 0c 24 <4c> 89 34 c2 e8 41 f2 ff ff 49 89 c6 48 85 c0 75 8c 48 8b 44 24 10
> <4> [188.935583] RSP: 0018:ffffc900011dbcc8 EFLAGS: 00010202
> <4> [188.935593] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 0000000000000001
> <4> [188.935603] RDX: 0000000000000010 RSI: ffffffff822e343c RDI: ffffc900011dbcc8
> <4> [188.935613] RBP: ffffc900011dbd48 R08: ffff88812d255bb8 R09: 00000000fffffffe
> <4> [188.935623] R10: 0000000000000001 R11: 0000000000000000 R12: ffffc900011dbd44
> <4> [188.935633] R13: ffffc900011dbd50 R14: ffff888113d29cc0 R15: 0000000000000000
> <4> [188.935643] FS: 00007f68d17e9700(0000) GS:ffff888277900000(0000) knlGS:0000000000000000
> <4> [188.935655] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4> [188.935665] CR2: 0000000000000010 CR3: 000000012d0a4000 CR4: 00000000003506e0
> <4> [188.935676] Call Trace:
> <4> [188.935685] i915_gem_object_wait+0x1ff/0x410 [i915]
> <4> [188.935988] i915_gem_wait_ioctl+0xf2/0x2a0 [i915]
> <4> [188.936272] ? i915_gem_object_wait+0x410/0x410 [i915]
> <4> [188.936533] drm_ioctl_kernel+0xae/0x140
> <4> [188.936546] drm_ioctl+0x201/0x3d0
> <4> [188.936555] ? i915_gem_object_wait+0x410/0x410 [i915]
> <4> [188.936820] ? __fget_files+0xc2/0x1c0
> <4> [188.936830] ? __fget_files+0xda/0x1c0
> <4> [188.936839] __x64_sys_ioctl+0x6d/0xa0
> <4> [188.936848] do_syscall_64+0x3a/0xb0
> <4> [188.936859] entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> If the shared object has changed during the RCU unlocked period
> callers will correctly handle the restart on the next iteration.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Fixes: 96601e8a4755 ("dma-buf: use new iterator in dma_resv_copy_fences")
> Fixes: d3c80698c9f5 ("dma-buf: use new iterator in dma_resv_get_fences v3")
> Closes: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Fintel%2F-%2Fissues%2F4274&data=04%7C01%7Cchristian.koenig%40amd.com%7C0a73b5d07f5f44cdc5a808d98a4109f9%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637692834972816537%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=jhcO2Q8bGhLTW7b4%2BNn4TE3UCwBbAcQVuceJEwDK0fg%3D&reserved=0
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: linux-media at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: linaro-mm-sig at lists.linaro.org
Maybe we should remove cursor->fences altogether, but either way the
patch is Reviewed-by: Christian König <christian.koenig at amd.com>
Please push to drm-misc-next ASAP.
Thanks,
Christian.
> ---
> drivers/dma-buf/dma-resv.c | 18 ++++++++++--------
> include/linux/dma-resv.h | 5 ++++-
> 2 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index a480af9581bd..7b6d881c8904 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -333,10 +333,14 @@ static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor)
> {
> cursor->seq = read_seqcount_begin(&cursor->obj->seq);
> cursor->index = -1;
> - if (cursor->all_fences)
> + cursor->shared_count = 0;
> + if (cursor->all_fences) {
> cursor->fences = dma_resv_shared_list(cursor->obj);
> - else
> + if (cursor->fences)
> + cursor->shared_count = cursor->fences->shared_count;
> + } else {
> cursor->fences = NULL;
> + }
> cursor->is_restarted = true;
> }
>
> @@ -363,7 +367,7 @@ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor)
> continue;
>
> } else if (!cursor->fences ||
> - cursor->index >= cursor->fences->shared_count) {
> + cursor->index >= cursor->shared_count) {
> cursor->fence = NULL;
> break;
>
> @@ -448,10 +452,8 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src)
> dma_resv_list_free(list);
> dma_fence_put(excl);
>
> - if (cursor.fences) {
> - unsigned int cnt = cursor.fences->shared_count;
> -
> - list = dma_resv_list_alloc(cnt);
> + if (cursor.shared_count) {
> + list = dma_resv_list_alloc(cursor.shared_count);
> if (!list) {
> dma_resv_iter_end(&cursor);
> return -ENOMEM;
> @@ -522,7 +524,7 @@ int dma_resv_get_fences(struct dma_resv *obj, struct dma_fence **fence_excl,
> if (fence_excl)
> dma_fence_put(*fence_excl);
>
> - count = cursor.fences ? cursor.fences->shared_count : 0;
> + count = cursor.shared_count;
> count += fence_excl ? 0 : 1;
>
> /* Eventually re-allocate the array */
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index 8b6c20636a79..3e1bff147428 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -170,9 +170,12 @@ struct dma_resv_iter {
> /** @index: index into the shared fences */
> unsigned int index;
>
> - /** @fences: the shared fences */
> + /** @fences: the shared fences; private, *MUST* not dereference */
> struct dma_resv_list *fences;
>
> + /** @shared_count: number of shared fences */
> + unsigned int shared_count;
> +
> /** @is_restarted: true if this is the first returned fence */
> bool is_restarted;
> };
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