{"id":"CVE-2026-52969","summary":"KVM: Reject wrapped offset in kvm_reset_dirty_gfn()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Reject wrapped offset in kvm_reset_dirty_gfn()\n\nkvm_reset_dirty_gfn() guards the gfn range with\n\n\tif (!memslot || (offset + __fls(mask)) \u003e= memslot-\u003enpages)\n\t\treturn;\n\nbut offset is u64 and the addition is unchecked.  The check can be\nsilently bypassed by a u64 wrap.\n\nThe dirty ring backing those entries is MAP_SHARED at\nKVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the\nslot and offset fields of any entry between when the kernel pushes\nthem and when KVM_RESET_DIRTY_RINGS consumes them.  On reset,\nkvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds\nthem straight back into this check; only the flags handshake is\ntreated as the handover, the slot/offset payload is taken on trust.\n\nCrafting two entries\n\n\tentry[i].offset   = 0xffffffffffffffc1\n\tentry[i+1].offset = 0\n\nmakes the coalescing loop in kvm_dirty_ring_reset() compute\n\n\tdelta = (s64)(0 - 0xffffffffffffffc1) = 63\n\nwhich falls in [0, BITS_PER_LONG), so it folds entry[i+1] into the\nexisting mask by setting bit 63.  The trailing kvm_reset_dirty_gfn()\ncall then sees offset = 0xffffffffffffffc1 and __fls(mask) = 63;\nthe sum is 0 in u64 and the bounds check passes.\n\nThat offset propagates into kvm_arch_mmu_enable_log_dirty_pt_masked()\nunchanged.  On the legacy MMU path -- kvm_memslots_have_rmaps() ==\ntrue, i.e. shadow paging, any VM that has allocated shadow roots, or\na write-tracked slot -- it reaches gfn_to_rmap(), which indexes\nslot-\u003earch.rmap[0][] with a near-U64_MAX gfn.  That is an\nout-of-bounds load of a kvm_rmap_head, followed by a conditional\nclear of PT_WRITABLE_MASK in whatever the loaded pointer points at.\nThe path is reachable from any process holding /dev/kvm.\n\nRange-check offset on its own first, so the addition cannot wrap.\nmemslot-\u003enpages is bounded well below U64_MAX, so once offset \u003c\nnpages holds, offset + __fls(mask) (with __fls(mask) \u003c BITS_PER_LONG)\nstays in range.","modified":"2026-07-11T09:29:26.030071994Z","published":"2026-06-24T16:28:48.085Z","related":["SUSE-SU-2026:22521-1","SUSE-SU-2026:22522-1","SUSE-SU-2026:2799-1","SUSE-SU-2026:2800-1","SUSE-SU-2026:2840-1","SUSE-SU-2026:2841-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52969.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/01b71b930f15728aa8599478a7ce90c19dcd9fc2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/0d419c23bb11b5c9664de777c47c1f04a235882d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/0eb281eb95b2d4eea4db1da5fe91023aecc97095"},{"type":"WEB","url":"https://git.kernel.org/stable/c/577a8d3bae0531f0e5ccfac919cd8192f920a804"},{"type":"WEB","url":"https://git.kernel.org/stable/c/74f1a22f7a80f03d28ad8551a2d25d563433addf"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b315b033a877b1ee6d827810b5d7bb4392ffcf8d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ecf9b3ea7847fe14f34b8c41f00de1eb95c747da"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52969.json"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-52969"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52969.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-52969"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2492434"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"fb04a1eddb1a65b6588a021bdc132270d5ae48bb"},{"fixed":"74f1a22f7a80f03d28ad8551a2d25d563433addf"},{"fixed":"0eb281eb95b2d4eea4db1da5fe91023aecc97095"},{"fixed":"01b71b930f15728aa8599478a7ce90c19dcd9fc2"},{"fixed":"b315b033a877b1ee6d827810b5d7bb4392ffcf8d"},{"fixed":"0d419c23bb11b5c9664de777c47c1f04a235882d"},{"fixed":"ecf9b3ea7847fe14f34b8c41f00de1eb95c747da"},{"fixed":"577a8d3bae0531f0e5ccfac919cd8192f920a804"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52969.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.209"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.175"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.141"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.91"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.33"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52969.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}