Re: [PATCH v4 1/4] hwmon: (pmbus) Add and export direct conversion calculation helpers

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Unchecked arithmetic operations in the exported helpers can silently overflow, violating the hardware monitoring subsystem guidelines.
--

commit 4b7c4efa13e04ccc1fad0afa9ecc064091eda152
Author: Stoyan Bogdanov <sbogdanov@baylibre.com>

hwmon: (pmbus) Add and export direct conversion calculation helpers

This commit splits the math-only parts of pmbus_reg2data_direct() and
pmbus_data2reg_direct() into separate helper functions. It exports these
helpers so they can be reused by upcoming drivers.

> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index e8fdd799c71c0..2eaac337eeaba 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c

[ ... ]

> @@ -1057,6 +1063,23 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data,
>  	return (mantissa & 0x7ff) | ((exponent << 11) & 0xf800);
>  }
>  
> +u16 pmbus_data2reg_direct_calc(s64 val, s64 b, s32 m, s32 R)
> +{
> +	val = val * m + b;

[Severity: High]
This is a pre-existing issue, but does this calculation need overflow checks
to conform with the hardware monitoring subsystem guidelines?

Since sysfs handlers can parse arbitrary 64-bit values from user space without
prior bounds checking, writing a very large positive value could overflow s64
during multiplication.

If an overflow wraps the value to a negative number, it would bypass the
intended clamping logic later in this function and result in writing S16_MIN
instead of S16_MAX to the hardware limit register.

For power management controllers, this unintended minimum limit could
immediately trip hardware protection and shut down the system.

> +
> +	while (R > 0) {
> +		val *= 10;
> +		R--;
> +	}
> +	while (R < 0) {
> +		val = div_s64(val + 5LL, 10L);  /* round closest */
> +		R++;
> +	}
> +
> +	return (u16)clamp_val(val, S16_MIN, S16_MAX);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260522082349.2749970-1-sbogdanov@baylibre.com?part=1