CVE-2026-43331 — x86/kexec: Disable KCOV instrumentation after load_segments()

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

x86/kexec: Disable KCOV instrumentation after load_segments()

The load_segments() function changes segment registers, invalidating GS base (which KCOV relies on for per-cpu data). When CONFIG_KCOV is enabled, any subsequent instrumented C code call (e.g. native_gdt_invalidate()) begins crashing the kernel in an endless loop.

To reproduce the problem, it's sufficient to do kexec on a KCOV-instrumented kernel:

$ kexec -l /boot/otherKernel $ kexec -e

The real-world context for this problem is enabling crash dump collection in syzkaller. For this, the tool loads a panic kernel before fuzzing and then calls makedumpfile after the panic. This workflow requires both CONFIG_KEXEC and CONFIG_KCOV to be enabled simultaneously.

Adding safeguards directly to the KCOV fast-path (__sanitizer_cov_trace_pc()) is also undesirable as it would introduce an extra performance overhead.

Disabling instrumentation for the individual functions would be too fragile, so disable KCOV instrumentation for the entire machine_kexec_64.c and physaddr.c. If coverage-guided fuzzing ever needs these components in the future, other approaches should be considered.

The problem is not relevant for 32 bit kernels as CONFIG_KCOV is not supported there.

[ bp: Space out comment for better readability. ]

USN-8903-1 — linux, linux-aws, linux-aws-6.8, linux-aws-fips, linux-fips, linux-realtime, linux-realtime-6.8 vulnerabilities

Affected: Ubuntu:22.04:LTS: linux-aws-6.8, Ubuntu:Pro:Realtime:22.04:LTS: linux-realtime-6.8, Ubuntu:24.04:LTS: linux, Ubuntu:24.04:LTS: linux-aws, Ubuntu:Pro:Realtime:24.04:LTS: linux-realtime, Ubuntu:Pro:FIPS-updates:24.04:LTS: linux-aws-fips, Ubuntu:Pro:FIPS-updates:24.04:LTS: linux-fips

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM32 architecture; - ARM64 architecture; - MIPS architecture; - x86 architecture; - Intel NPU Driver; - Auxiliary display drivers; - Compressed RAM block device driver; - GPIO subsystem; - GPU drivers; - HID subsystem; - I2C subsystem; - IIO subsystem; - InfiniBand drivers; - Input Device core drivers; - Input Device (Mouse) drivers; - Multiple devices driver; - Media drivers; - Fastrpc Driver; - Ethernet bonding driver; - Network drivers; - Mellanox network drivers; - Microsoft Azure Network Adapter (MANA) driver; - Texas Instruments network drivers; - NVMEM (Non Volatile Memory) drivers; - Parport drivers; - SCSI subsystem; - SLIMbus drivers; - NVIDIA Tegra SoC drivers; - SPI subsystem; - Trusted Execution Environment drivers; - Thunderbolt and USB4 drivers; - TTY drivers; - USB Device Class drivers; - DesignWare USB2 driver; - USB Gadget drivers; - USB Dual Role (OTG-ready) Controller drivers; - USB Serial drivers; - USB Type-C support driver; - USB Type-C Port Controller Manager driver; - USB Type-C Connector System Software Interface driver; - USB over IP driver; - Framebuffer layer; - Ext4 file system; - FUSE (File system in Userspace); - File systems infrastructure; - SMB network file system; - M…

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CVE-2026-43331 — x86/kexec: Disable KCOV instrumentation after load_segments()

USN-8903-1 — linux, linux-aws, linux-aws-6.8, linux-aws-fips, linux-fips, linux-realtime, linux-realtime-6.8 vulnerabilities