CVE-2026-64512

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

ACPI: CPPC: Suppress UBSAN warning caused by field misuse

The definition of reg->access_width changes depending on the
reg->space_id type. Type ACPI_ADR_SPACE_PLATFORM_COMM uses
access_width 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/cppc_acpi.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)
ubsan_epilogue+0x10/0x48
__ubsan_handle_shift_out_of_bounds+0xdc/0x1e0
cpc_write+0x4d0/0x670
cppc_set_perf+0x18c/0x490
cppc_cpufreq_cpu_init+0x1c8/0x380 [cppc_cpufreq]
... (trimming)

Lets fix this by validating the region type, as well as whether
access_width has a value. Then since we are returning bit_width
directly for ACPI_ADR_SPACE_PLATFORM_COMM, drop the code correcting
the size.