CVE-2026-43363

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> x86/apic: Disable x2apic on resume if the kernel expects so<br /> <br /> When resuming from s2ram, firmware may re-enable x2apic mode, which may have<br /> been disabled by the kernel during boot either because it doesn&amp;#39;t support IRQ<br /> remapping or for other reasons. This causes the kernel to continue using the<br /> xapic interface, while the hardware is in x2apic mode, which causes hangs.<br /> This happens on defconfig + bare metal + s2ram.<br /> <br /> Fix this in lapic_resume() by disabling x2apic if the kernel expects it to be<br /> disabled, i.e. when x2apic_mode = 0.<br /> <br /> The ACPI v6.6 spec, Section 16.3 [1] says firmware restores either the<br /> pre-sleep configuration or initial boot configuration for each CPU, including<br /> MSR state:<br /> <br /> When executing from the power-on reset vector as a result of waking from an<br /> S2 or S3 sleep state, the platform firmware performs only the hardware<br /> initialization required to restore the system to either the state the<br /> platform was in prior to the initial operating system boot, or to the<br /> pre-sleep configuration state. In multiprocessor systems, non-boot<br /> processors should be placed in the same state as prior to the initial<br /> operating system boot.<br /> <br /> (further ahead)<br /> <br /> If this is an S2 or S3 wake, then the platform runtime firmware restores<br /> minimum context of the system before jumping to the waking vector. This<br /> includes:<br /> <br /> CPU configuration. Platform runtime firmware restores the pre-sleep<br /> configuration or initial boot configuration of each CPU (MSR, MTRR,<br /> firmware update, SMBase, and so on). Interrupts must be disabled (for<br /> IA-32 processors, disabled by CLI instruction).<br /> <br /> (and other things)<br /> <br /> So at least as per the spec, re-enablement of x2apic by the firmware is<br /> allowed if "x2apic on" is a part of the initial boot configuration.<br /> <br /> [1] https://uefi.org/specs/ACPI/6.6/16_Waking_and_Sleeping.html#initialization<br /> <br /> [ bp: Massage. ]