UBUNTU-CVE-2026-64512: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: ACPI: CPPC: Suppress UBSAN warning caused by field misuse The definition of reg->accesswidth changes depending on the reg->spaceid type. Type ACPIADRSPACEPLATFORMCOMM uses accesswidth to indicate the PCC region, which can result in a UBSAN if the value is greater than 4. For example: UBSAN: shift-out-of-bounds in drivers/acpi/cppcacpi.c:1090:9 shift exponent 32 is too large for 32-bit type 'int' CPU: 61 UID: 0 PID: 1220 Comm: (udev-worker) Not tainted 7.0.10-201.fc44.aarch64 #1 PREEMPT(lazy) Hardware name: To be filled by O.E.M. Call trace: ...(trimming) ubsanepilogue+0x10/0x48 ubsanhandleshiftoutofbounds+0xdc/0x1e0 cpcwrite+0x4d0/0x670 cppcsetperf+0x18c/0x490 cppccpufreqcpuinit+0x1c8/0x380 [cppccpufreq] ... (trimming) Lets fix this by validating the region type, as well as whether accesswidth has a value. Then since we are returning bitwidth directly for ACPIADRSPACEPLATFORMCOMM, drop the code correcting the size.
Affected Software
Remediation
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1 - Compensating control
In the ACPI CPPC handling code, validate the region type before interpreting reg->access_width, ensure access_width has a value, and for ACPI_ADR_SPACE_PLATFORM_COMM return bit_width directly without applying the size-correction logic.
Event History
Frequently Asked Questions
Which systems are most likely to encounter this issue?
Systems using the affected Ubuntu kernel packages and ACPI CPPC CPU performance control are the relevant population. The described trigger involves an ACPI Platform Communications Channel (PCC) register whose access_width value is greater than 4.
What is required to trigger the warning?
The system must process an ACPI CPPC register with space_id ACPI_ADR_SPACE_PLATFORM_COMM and an access_width value that leads to an oversized shift. The example trace shows this occurring during cppc_cpufreq initialization from a udev worker.
How can I tell whether a system has encountered it?
Look for a UBSAN shift-out-of-bounds report referencing drivers/acpi/cppc_acpi.c, particularly a message that a shift exponent of 32 is too large for a 32-bit int. Relevant stack frames include cpc_write, cppc_set_perf, and cppc_cpufreq_cpu_init.
What does the fix change?
The fix validates the ACPI register region type and checks whether access_width has a value before using it. For Platform Communications Channel regions, it returns bit_width directly rather than applying the prior size-correction logic.