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platform/x86/amd/hsmp: Reject negative power cap writes in hwmon

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hsmp_hwmon_write() takes the user-supplied hwmon value as a signed long
and assigns "val / MICROWATT_PER_MILLIWATT" to msg.args[0], which is a
__u32.  MICROWATT_PER_MILLIWATT is an unsigned long, so a negative write
to power1_cap (e.g. "echo -1 > power1_cap") is first converted to a huge
unsigned value by the division and then stored into the u32 argument.

As a result a nonsensical, multi-gigawatt socket power limit is sent to
the SMU via HSMP_SET_SOCKET_POWER_LIMIT instead of the write being
rejected.

Reject negative values with -EINVAL before the conversion.

Tested with HSMP enabled:

  CAP=$(dirname $(grep -l amd_hsmp_hwmon \
        /sys/class/hwmon/hwmon*/name | head -1))/power1_cap

  # negative write
  echo -1000000 > $CAP ; echo "ret=$?"
  # valid positive write must still work
  echo 400000000 > $CAP ; echo "ret=$?"

Before:
  # echo -1000000 > $CAP ; echo "ret=$?"
  ret=0                             <- accepted; bogus limit sent to SMU
  # echo 400000000 > $CAP ; echo "ret=$?"
  ret=0

After:
  # echo -1000000 > $CAP ; echo "ret=$?"
  bash: echo: write error: Invalid argument
  ret=1                             <- rejected with -EINVAL
  # echo 400000000 > $CAP ; echo "ret=$?"
  ret=0                             <- valid write still works

Fixes: 92c025db52 ("platform/x86/amd/hsmp: Report power via hwmon sensors")
Signed-off-by: Hemanth Selam <hemanth.selam@gmail.com>
Link: https://patch.msgid.link/20260812090012.140193-1-hemanth.selam@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
This commit is contained in:
Hemanth Selam 2026-08-12 14:30:12 +05:30 committed by Ilpo Järvinen
parent 05c808362e
commit 3921bb8635
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1 changed files with 3 additions and 0 deletions
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3
drivers/platform/x86/amd/hsmp/hwmon.c
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@ -31,6 +31,9 @@ static int hsmp_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
if (attr != hwmon_power_cap)
return -EOPNOTSUPP;
if (val < 0)
return -EINVAL;
msg.num_args = 1;
msg.args[0] = val / MICROWATT_PER_MILLIWATT;
msg.msg_id = HSMP_SET_SOCKET_POWER_LIMIT;