riscv: futex: untag the user pointer before the atomic access

{
  "id": "06882651df0062fe23e089021958471cbb9d3b03185384c5303a3d2102303864",
  "url": "https://osv.dev/vulnerability/CVE-2026-99016",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "riscv: futex: untag the user pointer before the atomic access",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: riscv: futex: untag the user pointer before the atomic access access_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm amoswap/amoadd/.../lr.w+sc.w through the \"+m\" (*uaddr) operand. When the tagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl PR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a user pointer whose top PMLEN bits hold a tag passes access_ok() after untagging, but the atomic is then performed on the still-tagged raw address. Supervisor-mode data accesses are not subject to the U-mode pointer masking (that is governed by menvcfg.PMM, which the kernel does not set), so hardware does not strip the tag for the kernel's own access. With Sv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a tagged pointer can name a canonical kernel virtual address (e.g. in the linear map) whose untagged form is a valid user address. An unprivileged process can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on an arbitrary kernel address, with the matching FUTEX_OP_CMP_* result serving as a read oracle. get_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer after the access_ok() check; do the same in the futex helpers so the atomic operates on the address that was actually validated.",
    "evidence": "osv:CVE-2026-99016",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.57",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.11",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-99016",
      "aliases": [
        "CVE-2026-99016"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "2e1743085887ba3f553c2bb472a75a3ff744b242"
                },
                {
                  "fixed": "2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d"
                },
                {
                  "fixed": "8e48d8d51ab37b7decfbff3e2844e027a52ad6ea"
                },
                {
                  "fixed": "405290be962b32eec842776fbe3bdf81f15b1676"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-99016.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.57"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.11"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-99016.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.157299692Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d",
        "https://git.kernel.org/stable/c/405290be962b32eec842776fbe3bdf81f15b1676",
        "https://git.kernel.org/stable/c/8e48d8d51ab37b7decfbff3e2844e027a52ad6ea",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99016.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-99016",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99016.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-99016",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 522252,
  "published_at": "2026-10-23T12:20:47.859+00:00"
}