Linux is a mostly free kernel similar to the Unix kernel. It is one of the main examples of free and open source software.
After two months of development, Linus Torvalds announced the release of Linux Kernel 6.2, where the most notable changes include Copyleft-Next licensed code, improved RAID5/6 implementation in Btrfs, continued to integrate Rust language support, reduced Retbleed protection overhead, added limitation of memory rewriting and a TCP mechanism has been added. PLB (Protective Load Balancing) has been added.
The new version received 16843 fixes from 2178 developers, patch size is 62 MB (changes affected 14108 files, added 730195 lines of code, removed 409485 lines). About 42% of all changes introduced in 6.2 are associated with device drivers, about 16% of the changes are related to updating code specific to hardware architectures.
Main news in Linux 6.2
In this new version that is presented including the code and changes provided is permitted under the Copyleft-Next 0.3.1 license. The Copyleft-Next license was created by one of the GPLv3 contributors and is fully compatible with the GPLv2 license, as verified by SUSE and Red Hat lawyers. Compared to GPLv2, the Copyleft-Next license is much more compact and easy to understand (removed the introductory part and mention of deprecated commitments), determines the time and procedure for removing violations, automatically removes copyleft requirements for the when obsolete, which is more than 15 years.
Another change that stands out is that the “rv” utility is included, which provides an interface to interact from the user space with the handlers of the RV subsystem (Runtime Verification). Validation is performed at runtime by attaching controllers to tracepoints that verify the actual progress of the execution against a default reference deterministic automaton model that defines the expected behavior of the system.
Added the "iommufd" API for I/O Memory Management Unit (Memory Management Unit) user space management. The new API allows you to manage I/O memory page tables using file descriptors.
For the locking mechanism RCU (read-copy-update), an optional callback mechanism is implemented in which a timer processes multiple return calls at once in batch mode. Applying the proposed optimization allows to reduce power consumption on Android and ChromeOS devices by 5-10% by deferring RCU requests during idle or low system load.
Added a new option kernel command line "trace_trigger" to trigger a trace trigger which is used to bind conditional commands that are called when a stack trace is triggered (for example, trace_trigger=”sched_switch.stacktrace if prev_state == 2”).
Another change that stands out is that a port of additional functionality has been started from the Rust-for-Linux branch Related to the use of Rust as a second language for developing drivers and kernel modules. Rust support is disabled by default and does not cause Rust to be included as a required kernel build dependency. The basic functionality offered in the latest version is extended with features to support low-level code, such as the Vec type and the pr_debug!(), pr_cont!() and pr_alert!() macros, as well as the "#[vtable ]" macros. », procedural macro, which simplifies working with tables of pointers over functions. High-level Rust wrappers on top of the kernel subsystems are expected to be added in future releases, allowing you to build complete drivers in Rust.
In addition to this, it is also highlighted that implemented a new method to protect against the Retbleed vulnerability in Intel and AMD CPUs using call depth tracing, which is not as slow as the Retbleed protection present above. To enable the new mode, the kernel command line parameter “retbleed=stuff” is proposed.
En the platform ARM64, in the boot stage, it is possible to enable and disable the software implementation of the Shadow Stack mechanism, which is used to protect against overwriting of the return address of a function in case of stack buffer overflow (the gist of protection is to save the return address on a separate stack after passing control to the function and recovering the address given before exiting the function).
Of the other changes that stand out:
- For IPv6, added support for PLB (Protective Load Balancing), by changing the IPv6 flow label, the PLB randomly changes the packet routes to balance the load across the switch ports.
- Added support for 800 gigabit links.
- Added the ability to rename network interfaces on the fly, without stopping work.
- Added a mention of the IP address the packet arrived at to the SYN flood messages written to the log.
- For UDP, the ability to use separate hash tables for different network namespaces is implemented.
- Network bridges support the MAB (MAC Authentication Bypass) authentication method.
- The i915 (Intel) driver stabilized support for Intel Arc (DG2/Alchemist) discrete graphics cards and improved support for Meteor Lake GPUs.
- The Nouveau driver supports the NVIDIA GA102 (RTX 30) GPU based on the Ampere architecture. For nva3 (GT215) cards, the ability to control the backlight has been added.
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