linux-kernel - Re: [PATCH] thermal/x86_pkg_temp_thermal: Add lower bound check for sysfs input

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Date:   Fri, 17 Mar 2023 19:23:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Zhang Rui <rui.zhang@...el.com>
Cc:     linux-pm@...r.kernel.org, rafael.j.wysocki@...el.com,
        daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org,
        error27@...il.com, srinivas.pandruvada@...el.com
Subject: Re: [PATCH] thermal/x86_pkg_temp_thermal: Add lower bound check for
 sysfs input

On Wed, Mar 8, 2023 at 4:12 AM Zhang Rui <rui.zhang@...el.com> wrote:
>
> When setting a trip point temperature from sysfs, there is an upper
> bound check on the user input, but no lower bound check.
>
> As hardware register has 7 bits for a trip point temperature, the offset
> to tj_max of the input temperature must be equal to/less than 0x7f.
> Or else,
> 1. bogus temperature is updated into the trip temperature bits.
> 2. the upper bits of the register can be polluted.
>
> For example,
> $ rdmsr 0x1b2
> 2000003
> $ echo -180000 > /sys/class/thermal/thermal_zone1/trip_point_1_temp
> $ rdmsr 0x1b2
> 3980003
>
> Not only the trip point temp is set to 76C on this platform (tj_max is
> 100), the Power Notification (Bit 24) is also enabled erronously.
>
> Fix the problem by adding lower bound check for sysfs input.
>
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://lore.kernel.org/all/add7a378-4d50-4ba1-81d3-a0c17db25a0b@kili.mountain/
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> ---
> Note that I didn't add a Fixes tag here because this problem always
> exists, and even the location of this file has been changed.
>
> Note that I didn't cc -stable because this patch doesn't apply to older
> kernels due to recent changes. If Rafael thinks this is a stable
> material, we can rebase this fix on previous kernel after this patch
> hits upstream.
> ---
>  drivers/thermal/intel/x86_pkg_temp_thermal.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/thermal/intel/x86_pkg_temp_thermal.c b/drivers/thermal/intel/x86_pkg_temp_thermal.c
> index 1c2de84742df..128ee02596ed 100644
> --- a/drivers/thermal/intel/x86_pkg_temp_thermal.c
> +++ b/drivers/thermal/intel/x86_pkg_temp_thermal.c
> @@ -124,14 +124,16 @@ sys_set_trip_temp(struct thermal_zone_device *tzd, int trip, int temp)
>  {
>         struct zone_device *zonedev = tzd->devdata;
>         u32 l, h, mask, shift, intr;
> -       int tj_max, ret;
> +       int tj_max, val, ret;
>
>         tj_max = intel_tcc_get_tjmax(zonedev->cpu);
>         if (tj_max < 0)
>                 return tj_max;
>         tj_max *= 1000;
>
> -       if (trip >= MAX_NUMBER_OF_TRIPS || temp >= tj_max)
> +       val = (tj_max - temp)/1000;
> +
> +       if (trip >= MAX_NUMBER_OF_TRIPS || val < 0 || val > 0x7f)
>                 return -EINVAL;
>
>         ret = rdmsr_on_cpu(zonedev->cpu, MSR_IA32_PACKAGE_THERM_INTERRUPT,
> @@ -156,7 +158,7 @@ sys_set_trip_temp(struct thermal_zone_device *tzd, int trip, int temp)
>         if (!temp) {
>                 l &= ~intr;
>         } else {
> -               l |= (tj_max - temp)/1000 << shift;
> +               l |= val << shift;
>                 l |= intr;
>         }
>
> --

Applied as 6.4 material, thanks!