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Kernel: BPF, Extendable Read-Only File System and Display Core Next

Submitted by Roy Schestowitz on Thursday 29th of August 2019 04:35:39 AM Filed under
Graphics/Benchmarks
Linux
  • Reconsidering unprivileged BPF

    The BPF virtual machine within the kernel has seen a great deal of work over the last few years; as that has happened, its use has expanded to many different kernel subsystems. One of the objectives of that work in the past has been to make it safe to allow unprivileged users to load at least some types of BPF programs into the kernel. A recent discussion has made it clear, though, that the goal of opening up BPF to unprivileged users has been abandoned as unachievable, and that further work in that direction will not be accepted by the BPF maintainer.
    The BPF verifier goes to great lengths to ensure that any BPF program presented to the kernel is safe to run. Memory accesses are checked, execution is simulated to ensure that the program will terminate in a bounded period of time, and so on. Many of these checks are useful to ensure that all programs are safe and free of certain types of bugs, but others are aimed specifically at containing a potentially hostile program — an obvious necessity if the kernel is to accept BPF programs from unprivileged users.

    Much of this work was done in 2015 for the 4.4 kernel; in particular, a great deal of effort went into preventing BPF programs from leaking kernel pointer values to user space. Those pointers could be highly useful to an attacker who is trying to figure out where specific data structures or code are to be found on a target system, so making them easily available to unprivileged processes is clearly a bad idea. "Constant blinding" was added for 4.7. In essence, this mechanism will exclusive-OR constant values in programs with a random number (repeating the operation at run time when the values are actually used), preventing an attacker from sneaking in unverified BPF code disguised as constants. Other patches have been aimed at preventing speculative-execution attacks by BPF programs.

  • On-disk format robustness requirements for new filesystems

    The "Extendable Read-Only File System" (or "EROFS") was first posted by Gao Xiang in May 2018; it was merged into the staging tree for the 4.19 release. There has been a steady stream of work on EROFS since then, and its author now thinks that it is ready to move out of staging and join the other official filesystems in the kernel. It would seem, though, that there is one final hurdle that it may have to clear: robustness in the face of a corrupted on-disk filesystem image. That raises an interesting question: to what extent do new filesystems have to exhibit a level of robustness that is not met by the filesystems that are currently in heavy use?
    As suggested by its name (and its acronym), EROFS is a read-only filesystem. It was developed at Huawei, and is intended for use in Android systems. EROFS is meant to differ from existing read-only filesystems in the area of performance; it uses a special compression algorithm that creates fixed-length blocks that, it is claimed, allows random access to compressed data with a minimum of excess I/O and decompression work. Details can be found in this USENIX paper [PDF] published in July.

  • AMD Renoir APUs Bringing "DCN 2.1" Display Engine

    Raven Ridge APUs brought the DCN 1.0 "Display Core Next" engine, Navi GPUs upped that to a DCN 2.0 implementation for the display engine, and now the Renoir APUs are ushering in DCN 2.1. This is a bit interesting particularly with Renoir being a Vega-based GPU and not Navi as one would have hoped prior to the Vega confirmation in the earlier patches.

»

AMD Navi 14 Support To Be Backwards Compatible With Mesa 19.2

Submitted by Roy Schestowitz on Thursday 29th of August 2019 05:38:11 AM.
  • AMD Navi 14 Support To Be Backwards Compatible With Mesa 19.2 And Arrive In Lower-End Affordable Graphics Cards?

    AMD is yet to officially confirm its Navi 14 GPU. However, the AMD’s Navi 10 GPU which uses the RDNA 1.0 architecture and is made using a 7 nm production process at TSMC, could debut soon, indicated multiple entries. The Navi 10 GPU succeeds the ‘Polaris’ GPU, indicated a Linux driver and even the CompuBench database that appeared last month. It is interesting to note that AMD is expected to backport the Navi 14 support to the Mesa 3D Graphics Library. The Mesa3D’s Mesa 19.2 version, which could be released within the next 30 or so days, should include the support for the latest Navi 14 GPU.

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