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
CVSS
No CVSS.
References
Configurations
No configuration.
History
17 Sep 2026, 17:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-09-17 17:17
Updated : 2026-09-17 17:17
NVD link : CVE-2026-90136
Mitre link : CVE-2026-90136
CVE.ORG link : CVE-2026-90136
JSON object : View
Products Affected
No product.
CWE
No CWE.