In vc4_atomic_commit_tail() we iterate of the set of old CRTCs, and attempt to wait on any channels which are still in use. When we iterate over the CRTCs, we have: * `i` - the index of the CRTC * `channel` - the channel a CRTC is using When we check the channel state, we consult: old_hvs_state->fifo_state[channel].in_use ... but when we wait for the channel, we erroneously wait on: old_hvs_state->fifo_state[i].pending_commit ... rather than: old_hvs_state->fifo_state[channel].pending_commit ... and this bogus access has been observed to result in boot-time hangs on some arm64 configurations, and can be detected using KASAN. FIx this by using the correct index. I've tested this on a Raspberry Pi 3 model B v1.2 with KASAN. Trimmed KASAN splat: | ================================================================== | BUG: KASAN: slab-out-of-bounds in vc4_atomic_commit_tail+0x1cc/0x910 | Read of size 8 at addr ffff000007360440 by task kworker/u8:0/7 | CPU: 2 PID: 7 Comm: kworker/u8:0 Not tainted 5.13.0-rc3-00009-g694c523e7267 #3 | | Hardware name: Raspberry Pi 3 Model B (DT) | Workqueue: events_unbound deferred_probe_work_func | Call trace: | dump_backtrace+0x0/0x2b4 | show_stack+0x1c/0x30 | dump_stack+0xfc/0x168 | print_address_description.constprop.0+0x2c/0x2c0 | kasan_report+0x1dc/0x240 | __asan_load8+0x98/0xd4 | vc4_atomic_commit_tail+0x1cc/0x910 | commit_tail+0x100/0x210 | ... | | Allocated by task 7: | kasan_save_stack+0x2c/0x60 | __kasan_kmalloc+0x90/0xb4 | vc4_hvs_channels_duplicate_state+0x60/0x1a0 | drm_atomic_get_private_obj_state+0x144/0x230 | vc4_atomic_check+0x40/0x73c | drm_atomic_check_only+0x998/0xe60 | drm_atomic_commit+0x34/0x94 | drm_client_modeset_commit_atomic+0x2f4/0x3a0 | drm_client_modeset_commit_locked+0x8c/0x230 | drm_client_modeset_commit+0x38/0x60 | drm_fb_helper_set_par+0x104/0x17c | fbcon_init+0x43c/0x970 | visual_init+0x14c/0x1e4 | ... | | The buggy address belongs to the object at ffff000007360400 | which belongs to the cache kmalloc-128 of size 128 | The buggy address is located 64 bytes inside of | 128-byte region [ffff000007360400, ffff000007360480) | The buggy address belongs to the page: | page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7360 | flags: 0x3fffc0000000200(slab|node=0|zone=0|lastcpupid=0xffff) | raw: 03fffc0000000200 dead000000000100 dead000000000122 ffff000004c02300 | raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 | page dumped because: kasan: bad access detected | | Memory state around the buggy address: | ffff000007360300: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb | ffff000007360380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc | >ffff000007360400: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc | ^ | ffff000007360480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc | ffff000007360500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb | ================================================================== Link: https://lore.kernel.org/r/4d0c8318-bad8-2be7-e292-fc8f70c198de@xxxxxxxxxxx Link: https://lore.kernel.org/linux-arm-kernel/20210607151740.moncryl5zv3ahq4s@gilmour Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Daniel Vetter <daniel@xxxxxxxx> Cc: David Airlie <airlied@xxxxxxxx> Cc: Emma Anholt <emma@xxxxxxxxxx> Cc: Maxime Ripard <maxime@xxxxxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx --- drivers/gpu/drm/vc4/vc4_kms.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c index bb5529a7a9c2..948b3a58aad1 100644 --- a/drivers/gpu/drm/vc4/vc4_kms.c +++ b/drivers/gpu/drm/vc4/vc4_kms.c @@ -372,7 +372,7 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state) if (!old_hvs_state->fifo_state[channel].in_use) continue; - ret = drm_crtc_commit_wait(old_hvs_state->fifo_state[i].pending_commit); + ret = drm_crtc_commit_wait(old_hvs_state->fifo_state[channel].pending_commit); if (ret) drm_err(dev, "Timed out waiting for commit\n"); } -- 2.11.0
