GHSA-547R-P462-QV3C
Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-09-17 18:31In 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
{
"affected": [],
"aliases": [
"CVE-2026-90136"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:17:06Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nplatform/x86/amd/hsmp: Reject negative power cap writes in hwmon\n\nhsmp_hwmon_write() takes the user-supplied hwmon value as a signed long\nand assigns \"val / MICROWATT_PER_MILLIWATT\" to msg.args[0], which is a\n__u32. MICROWATT_PER_MILLIWATT is an unsigned long, so a negative write\nto power1_cap (e.g. \"echo -1 \u003e power1_cap\") is first converted to a huge\nunsigned value by the division and then stored into the u32 argument.\n\nAs a result a nonsensical, multi-gigawatt socket power limit is sent to\nthe SMU via HSMP_SET_SOCKET_POWER_LIMIT instead of the write being\nrejected.\n\nReject negative values with -EINVAL before the conversion.\n\nTested with HSMP enabled:\n\n CAP=$(dirname $(grep -l amd_hsmp_hwmon \\\n /sys/class/hwmon/hwmon*/name | head -1))/power1_cap\n\n # negative write\n echo -1000000 \u003e $CAP ; echo \"ret=$?\"\n # valid positive write must still work\n echo 400000000 \u003e $CAP ; echo \"ret=$?\"\n\nBefore:\n # echo -1000000 \u003e $CAP ; echo \"ret=$?\"\n ret=0 \u003c- accepted; bogus limit sent to SMU\n # echo 400000000 \u003e $CAP ; echo \"ret=$?\"\n ret=0\n\nAfter:\n # echo -1000000 \u003e $CAP ; echo \"ret=$?\"\n bash: echo: write error: Invalid argument\n ret=1 \u003c- rejected with -EINVAL\n # echo 400000000 \u003e $CAP ; echo \"ret=$?\"\n ret=0 \u003c- valid write still works",
"id": "GHSA-547r-p462-qv3c",
"modified": "2026-09-17T18:31:52Z",
"published": "2026-09-17T18:31:52Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90136"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1b0a3d915320f1600e5ff43f8bc21b73118480b8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2c09cadec116eba3fdbcb5d8d8641f6777d4a11f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3921bb8635ff2836622df1cdf3194d4f3c1835a4"
}
],
"schema_version": "1.4.0",
"severity": []
}
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