Description
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
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
Published:
2026-09-17
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
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Tracking
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Advisories
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References
History
Thu, 17 Sep 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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 | |
| Title | platform/x86/amd/hsmp: Reject negative power cap writes in hwmon | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-17T16:06:35.190Z
Reserved: 2026-09-11T19:38:34.788Z
Link: CVE-2026-90136
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-17T17:17:06.173
Modified: 2026-09-17T17:17:06.173
Link: CVE-2026-90136
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.