{"id":"CVE-2026-99016","title":"riscv: futex: untag the user pointer before the atomic access","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nriscv: futex: untag the user pointer before the atomic access\n\naccess_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser()\nand futex_atomic_cmpxchg_inato…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d","Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea","Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 405290be962b32eec842776fbe3bdf81f15b1676","Linux 6.13"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:20:47.859Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99016","references":[{"url":"https://git.kernel.org/stable/c/2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d"},{"url":"https://git.kernel.org/stable/c/8e48d8d51ab37b7decfbff3e2844e027a52ad6ea"},{"url":"https://git.kernel.org/stable/c/405290be962b32eec842776fbe3bdf81f15b1676"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.539Z","slug":"CVE-2026-99016","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nriscv: futex: untag the user pointer before the atomic access\n\naccess_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser()\nand futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm\namoswap/amoadd/.../lr.w+sc.w through the \"+m\" (*uaddr) operand.  When the\ntagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl\nPR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a\nuser pointer whose top PMLEN bits hold a tag passes access_ok() after\nuntagging, but the atomic is then performed on the still-tagged raw\naddress.\n\nSupervisor-mode data accesses are not subject to the U-mode pointer\nmasking (that is governed by menvcfg.PMM, which the kernel does not set),\nso hardware does not strip the tag for the kernel's own access.  With\nSv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a\ntagged pointer can name a canonical kernel virtual address (e.g. in the\nlinear map) whose untagged form is a valid user address.  An unprivileged\nprocess can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on\nan arbitrary kernel address, with the matching FUTEX_OP_CMP_* result\nserving as a read oracle.\n\nget_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer\nafter the access_ok() check; do the same in the futex helpers so the\natomic operates on the address that was actually validated.\n\n## Affected\n\n- `Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d`\n- `Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea`\n- `Linux >= 2e1743085887ba3f553c2bb472a75a3ff744b242 < 405290be962b32eec842776fbe3bdf81f15b1676`\n- `Linux 6.13`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}