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Date: Fri, 5 Jun 2026 09:33:41 -0700
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Cc: linux-acpi@vger.kernel.org, easwar.hariharan@linux.microsoft.com,
 jarredwhite@linux.microsoft.com, lenb@kernel.org, rafael@kernel.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ACPI: CPPC: Suppress UBSAN warning caused by field misuse
To: Jeremy Linton <jeremy.linton@arm.com>
References: <20260601235808.1113137-1-jeremy.linton@arm.com>
From: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
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In-Reply-To: <20260601235808.1113137-1-jeremy.linton@arm.com>
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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@arm.com>
> ---
>  drivers/acpi/cppc_acpi.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
Reviewed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>