Quoting Koenig, Christian (2019-08-24 20:04:43) > Am 24.08.19 um 15:58 schrieb Chris Wilson: > > In order to allow dma-fence-array as a generic container for fences, we > > need to allow for it to contain other dma-fence-arrays. By giving each > > dma-fence-array construction their own lockclass, we allow different > > types of dma-fence-array to nest, but still do not allow on class of > > dma-fence-array to contain itself (even though they have distinct > > locks). > > > > In practice, this means that each subsystem gets its own dma-fence-array > > class and we can freely use dma-fence-arrays as containers within the > > dmabuf core without angering lockdep. > > I've considered this for as well. E.g. to use the dma_fence_array > implementation instead of coming up with the dma_fence_chain container. > > But as it turned out when userspace can control nesting, it is trivial > to chain enough dma_fence_arrays together to cause an in kernel stack > overflow. Which in turn creates a really nice attack vector. > > So as long as userspace has control over dma_fence_array nesting this is > a clear NAK and actually extremely dangerous. You are proposing to use recursive dma_fence_array containers for dma_resv... > It actually took me quite a while to get the dma_fence_chain container > recursion less to avoid stuff like this. Sure, we've been avoiding recursion for years. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
