From 76250f2b743b72cb685cc51ac0cdabb32957180b Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 14 Feb 2017 12:40:01 +0000 Subject: [PATCH] dma-buf/fence: Avoid use of uninitialised timestamp [ 236.821534] WARNING: kmemcheck: Caught 64-bit read from uninitialized memory (ffff8802538683d0) [ 236.828642] 420000001e7f0000000000000000000000080000000000000000000000000000 [ 236.839543] i i i i u u u u i i i i i i i i u u u u u u u u u u u u u u u u [ 236.850420] ^ [ 236.854123] RIP: 0010:[] [] fence_signal+0x17/0xd0 [ 236.861313] RSP: 0018:ffff88024acd7ba0 EFLAGS: 00010282 [ 236.865027] RAX: ffffffff812f6a90 RBX: ffff8802527ca800 RCX: ffff880252cb30e0 [ 236.868801] RDX: ffff88024ac5d918 RSI: ffff880252f780e0 RDI: ffff880253868380 [ 236.872579] RBP: ffff88024acd7bc0 R08: ffff88024acd7be0 R09: 0000000000000000 [ 236.876407] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880253868380 [ 236.880185] R13: ffff8802538684d0 R14: ffff880253868380 R15: ffff88024cd48e00 [ 236.883983] FS: 00007f1646d1a740(0000) GS:ffff88025d000000(0000) knlGS:0000000000000000 [ 236.890959] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 236.894702] CR2: ffff880251360318 CR3: 000000024ad21000 CR4: 00000000001406f0 [ 236.898481] [] i915_gem_request_retire+0x1cd/0x230 [ 236.902439] [] i915_gem_request_alloc+0xa3/0x2f0 [ 236.906435] [] i915_gem_do_execbuffer.isra.41+0xb6d/0x18b0 [ 236.910434] [] i915_gem_execbuffer2+0x95/0x1e0 [ 236.914390] [] drm_ioctl+0x1e5/0x460 [ 236.918275] [] do_vfs_ioctl+0x8f/0x5c0 [ 236.922168] [] SyS_ioctl+0x3c/0x70 [ 236.926090] [] entry_SYSCALL_64_fastpath+0x17/0x93 [ 236.930045] [] 0xffffffffffffffff We only set the timestamp before we mark the fence as signaled. It is done before to avoid observers having a window in which they may see the fence as complete but no timestamp. Having it does incur a potential for the timestamp to be written twice, and even for it to be corrupted if the u64 write is not atomic. Instead use a new bit to record the presence of the timestamp, and teach the readers to wait until it is set if the fence is complete. There still remains a race where the timestamp for the signaled fence may be shown before the fence is reported as signaled, but that's a pre-existing error. Signed-off-by: Chris Wilson Cc: Sumit Semwal Cc: Gustavo Padovan Cc: Daniel Vetter Reported-by: Rafael Antognolli Signed-off-by: Gustavo Padovan Link: http://patchwork.freedesktop.org/patch/msgid/20170214124001.1930-1-chris@chris-wilson.co.uk --- drivers/dma-buf/dma-fence.c | 17 ++++++----------- drivers/dma-buf/sync_debug.c | 2 +- drivers/dma-buf/sync_file.c | 8 +++++++- include/linux/dma-fence.h | 2 ++ 4 files changed, 16 insertions(+), 13 deletions(-) diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0918d3f003d6..13556fdda2a5 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -75,11 +75,6 @@ int dma_fence_signal_locked(struct dma_fence *fence) if (WARN_ON(!fence)) return -EINVAL; - if (!ktime_to_ns(fence->timestamp)) { - fence->timestamp = ktime_get(); - smp_mb__before_atomic(); - } - if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) { ret = -EINVAL; @@ -87,8 +82,11 @@ int dma_fence_signal_locked(struct dma_fence *fence) * we might have raced with the unlocked dma_fence_signal, * still run through all callbacks */ - } else + } else { + fence->timestamp = ktime_get(); + set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags); trace_dma_fence_signaled(fence); + } list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) { list_del_init(&cur->node); @@ -115,14 +113,11 @@ int dma_fence_signal(struct dma_fence *fence) if (!fence) return -EINVAL; - if (!ktime_to_ns(fence->timestamp)) { - fence->timestamp = ktime_get(); - smp_mb__before_atomic(); - } - if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) return -EINVAL; + fence->timestamp = ktime_get(); + set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags); trace_dma_fence_signaled(fence); if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) { diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c index c769dc653b34..bfead12390f2 100644 --- a/drivers/dma-buf/sync_debug.c +++ b/drivers/dma-buf/sync_debug.c @@ -84,7 +84,7 @@ static void sync_print_fence(struct seq_file *s, show ? "_" : "", sync_status_str(status)); - if (status) { + if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags)) { struct timespec64 ts64 = ktime_to_timespec64(fence->timestamp); diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index 2321035f6204..95f259b719fc 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -375,7 +375,13 @@ static void sync_fill_fence_info(struct dma_fence *fence, sizeof(info->driver_name)); info->status = dma_fence_get_status(fence); - info->timestamp_ns = ktime_to_ns(fence->timestamp); + while (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) && + !test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags)) + cpu_relax(); + info->timestamp_ns = + test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags) ? + ktime_to_ns(fence->timestamp) : + ktime_set(0, 0); } static long sync_file_ioctl_fence_info(struct sync_file *sync_file, diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index a5195a7d6f77..0a186c4f3981 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -55,6 +55,7 @@ struct dma_fence_cb; * of the time. * * DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled + * DMA_FENCE_FLAG_TIMESTAMP_BIT - timestamp recorded for fence signaling * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called * DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the * implementer of the fence for its own purposes. Can be used in different @@ -84,6 +85,7 @@ struct dma_fence { enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, + DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, DMA_FENCE_FLAG_USER_BITS, /* must always be last member */ };