Linux 6.6 Kernel Released with Intel Shadow Stack and Other Improvements


The Linux kernel, the core component of the operating system that powers millions of devices around the world, has received a major update. Linus Torvalds, the creator and maintainer of the Linux kernel, announced the release of Linux 6.6 on October 29, 2023. This is the sixth major release of the year and brings several new features, updated and new drivers for better hardware support, and other changes.

Intel Shadow Stack: A New Security Feature for Intel CPUs

One of the most notable features of Linux 6.6 is the support for Intel Shadow Stack, a hardware security feature that protects Intel processors against stack-overwrite attacks. Stack-overwrite attacks are a type of exploit that can hijack the control flow of a program by overwriting the return address on the stack. Intel Shadow Stack prevents this by maintaining a separate, protected stack that stores only the return addresses. The processor checks the return address on both stacks before returning from a function call, and raises an exception if they do not match.

Linux 6.6 Kernel Released with Intel Shadow Stack and Other Improvements
Linux 6.6 Kernel Released with Intel Shadow Stack and Other Improvements

Intel Shadow Stack is part of Intel’s Control-flow Enforcement Technology (CET), which was introduced with Tiger Lake CPUs in 2020. Linux 6.6 is the first kernel version to support this feature, which requires both hardware and software support. Users who have compatible CPUs and want to enable Intel Shadow Stack need to compile their kernel with CONFIG_X86_INTEL_SHADOW_STACK option and use a CET-aware toolchain to build their user-space applications.

Better Support for HP and ASUS Devices

Linux 6.6 also improves the support for various HP and ASUS devices. For HP laptops, a new firmware-attributes driver has been added that allows users to change BIOS settings from within Linux. This driver supports HP laptops from 2018 and later and exposes a sysfs interface for modifying various options such as boot order, secure boot, TPM, fan speed, etc.

For ASUS laptops, Linux 6.6 adds support for changing charger mode, middle fan, and eGPU settings for ROG Flow X16 (2023) gaming laptops. These settings can be controlled via a new asus-wmi driver that also handles keyboard backlight control for more IdeaPad laptops.

Networking Improvements: New Hardware and Drivers

On the networking side of things, Linux 6.6 features support for new hardware such as Atheros QCA8081, MediaTek MT7988, MediaTek MT7981, NXP TJA1120 PHY, and more. Even the drivers have seen upgrades, such as the Qualcomm Wi-Fi 7 (ath12k) driver, which now supports Extremely High Throughput (EHT) PHY. EHT PHY is a new feature of Wi-Fi 7 that enables higher data rates and lower latency for wireless communication.

Another notable improvement is the enabling of AP mode for various Realtek (rtl8xxxu) Wi-Fi chips. AP mode allows users to create a wireless hotspot from their laptop or desktop and share their internet connection with other devices. This feature was previously unavailable for many Realtek chips due to firmware limitations.

AMD Enhancements: SEV-SNP, DBC, and More

Linux 6.6 also brings some enhancements for AMD users. One of them is the support for Secure Encrypted Virtualization – Secure Nested Paging (SEV-SNP), a new feature of AMD EPYC processors that enhances the security and performance of virtual machines. SEV-SNP encrypts both the memory and the page tables of virtual machines, preventing unauthorized access from the hypervisor or other guests.

Another feature is Dynamic Boost Control (DBC), which allows AMD Ryzen processors to dynamically adjust their power limits based on workload and temperature. DBC can improve the performance and efficiency of AMD CPUs by allowing them to boost higher when needed.

Linux 6.6 also adds support for two new pieces of technology that AMD has yet to officially announce: Van Gogh and Rembrandt APUs. Van Gogh is rumored to be a low-power APU for laptops that features Zen 2 CPU cores and RDNA 2 GPU cores. Rembrandt is expected to be a high-performance APU for laptops that features Zen 3+ CPU cores and RDNA 2 GPU cores.

Other Changes: File Systems, Sound Hardware, Stadia Controller Rumble, etc.

Linux 6.6 also includes many other changes that affect various aspects of the system. Some of them are:

  • File Systems: F2FS file system gains zoned block device and compression support improvements; FUSE file system gains support for shared mmaps in no-cache mode; tmpfs file system gains support for quota, direct I/O, and extended attributes; NFS server gains support for NFSv4 write delegations; SMB3 file system is declared stable.
  • Sound Hardware: Support for Cirrus Logic CS42L43 audio codec; support for USB MIDI 2 gadget; improved support for Sound Blaster ZxR cards.
  • Stadia Controller Rumble: Support for rumble feedback on Google Stadia controllers via hid-google driver.
  • NVIDIA T4 GPUs: Support for Secondary Bus Reset on NVIDIA T4 GPUs, which allows users to reset the GPU without rebooting the system.
  • io_uring: Initial support for network operations via io_uring, a high-performance and scalable I/O interface.

How to Get Linux 6.6

Linux 6.6 is available for download from the official kernel website or from Linus Torvalds’ Git tree. Users who want to try the new kernel need to compile it from source and install it on their system. Alternatively, they can wait for their Linux distribution to provide an update that includes Linux 6.6.

Linux 6.6 is a non-LTS release, which means that it will be supported for about two months until the next major release, Linux 6.7, arrives. Users who prefer stability and long-term support should stick to the LTS releases, such as Linux 5.15, which was released earlier this month and will be supported until 2025.


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