EUVD-2026-81729
GHSA-547r-p462-qv3c
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2DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
platform/x86/amd/hsmp: Reject negative power cap writes in hwmon
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
Analysis
In the Linux kernel, the following vulnerability has been resolved: platform/x86/amd/hsmp: Reject negative power cap writes in hwmon 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. …
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