CVE-2026-89928: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f7hc-2wxr-4jfg",
  "modified" : "2026-09-16T15:31:02Z",
  "published" : "2026-09-16T12:30:41Z",
  "aliases" : [ "CVE-2026-89928" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Consume the locked rmap value in the lockless rmap walk\n\n__kvm_rmap_lock() deliberately elides the rmap lock when it observes an\nempty rmap.  In that case kvm_rmap_lock_readonly() also re-enables\npreemption and returns zero, so the caller holds neither the rmap lock\nnor a preemption reference.  The elision documents the invariant it\nrelies on:\n\n\t * Elide the lock if the rmap is empty, as lockless walkers (read-only\n\t * mode) don't need to (and can't) walk an empty rmap, nor can they add\n\t * entries to the rmap.  I.e. the only paths that process empty rmaps\n\t * do so while holding mmu_lock for write, and are mutually exclusive.\n\nkvm_rmap_age_gfn_range() ignores the returned value and unconditionally\nenters for_each_rmap_spte_lockless().  The iterator started with\nrmap_get_first(), which re-reads rmap_head->val rather than using the\nvalue returned by the lock.  If a writer populates the rmap between the\nlock's read and the iterator's re-read, the aging path walks the newly\ninstalled rmap without holding its lock.\n\nFor a KVM_RMAP_MANY rmap this leaves the walker following a\npte_list_desc chain that it never locked.  A writer holding mmu_lock for\nwrite may free that chain (e.g. kvm_zap_all_rmap_sptes() on the recycle\npath, or any rmap zap) via kmem_cache_free() while the walk is in\nprogress, giving a slab use-after-free.  Nothing serialises the two: the\naging path runs without mmu_lock when CONFIG_KVM_MMU_LOCKLESS_AGING=y,\nand the rmap lock that would otherwise exclude the writer was elided.\nBecause the empty path re-enables preemption, the interval between the\ntwo reads can span an arbitrary scheduling delay.\n\nFix the class of bug by having the lockless walk consume the value\nreturned by the lock instead of re-reading the rmap.  Split\nrmap_get_first() into __rmap_get_first(), which starts an iterator from\nan already-read rmap value, and make for_each_rmap_spte_lockless() take\nthat value and call __rmap_get_first() directly.\nkvm_rmap_age_gfn_range() passes the value returned by\nkvm_rmap_lock_readonly(): when the lock was elided the value is zero,\n__rmap_get_first() returns NULL, and the walk is skipped.  No lockless\nwalker re-reads the rmap, so the lock-elision invariant cannot be\nviolated, and no lock()-without-paired-unlock() path is added to the\naging code.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-89928"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/41debfc98526c0a95c41a62435aca0a70340a26d"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/8edb3c09e43f7cd8a5dfd291c6e0fc9c74d4621d"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/e428f9779a43737d830111238816f1928b07aefb"
  } ],
  "database_specific" : {
    "cwe_ids" : [ ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-16T11:17:02Z"
  }
}