Re: [PATCH] ACPI: CPPC: Suppress UBSAN warning caused by field misuse

[Rafael J. Wysocki]

On Fri, Jun 5, 2026 at 6:33 PM Easwar Hariharan
<easwar.hariharan@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On 6/1/2026 16:58, Jeremy Linton wrote:
> > 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.
> >
> > Fixes: 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for system memory accesses")
> > Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> > ---
> >  drivers/acpi/cppc_acpi.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> >
> Reviewed-by: Easwar Hariharan <easwar.hariharan@xxxxxxxxxxxxxxxxxxx>

Applied as 7.2 material, thanks!