{"api_version":"1","generated_at":"2026-08-30T18:14:18+00:00","cve":"CVE-2025-40040","urls":{"html":"https://cve.report/CVE-2025-40040","api":"https://cve.report/api/cve/CVE-2025-40040.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2025-40040","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2025-40040"},"summary":{"title":"mm/ksm: fix flag-dropping behavior in ksm_madvise","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/ksm: fix flag-dropping behavior in ksm_madvise\n\nsyzkaller discovered the following crash: (kernel BUG)\n\n[   44.607039] ------------[ cut here ]------------\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\n\n<snip other registers, drop unreliable trace>\n\n[   44.617726] Call Trace:\n[   44.617926]  <TASK>\n[   44.619284]  userfaultfd_release+0xef/0x1b0\n[   44.620976]  __fput+0x3f9/0xb60\n[   44.621240]  fput_close_sync+0x110/0x210\n[   44.622222]  __x64_sys_close+0x8f/0x120\n[   44.622530]  do_syscall_64+0x5b/0x2f0\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[   44.623244] RIP: 0033:0x7f365bb3f227\n\nKernel panics because it detects UFFD inconsistency during\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\nto vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags.\n\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\nit accidentally clears all flags stored in the upper 32 bits of\nvma->vm_flags.\n\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\nint are 32-bit wide.  This setup causes the following mishap during the &=\n~VM_MERGEABLE assignment.\n\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. \nAfter ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then\npromoted to unsigned long before the & operation.  This promotion fills\nupper 32 bits with leading 0s, as we're doing unsigned conversion (and\neven for a signed conversion, this wouldn't help as the leading bit is 0).\n& operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff\ninstead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears\nthe upper 32-bits of its value.\n\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\nBIT() macro.\n\nNote: other VM_* flags are not affected: This only happens to the\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\nand after ~ operation, they end up with leading 1 and are thus converted\nto unsigned long with leading 1s.\n\nNote 2:\nAfter commit 31defc3b01d9 (\"userfaultfd: remove (VM_)BUG_ON()s\"), this is\nno longer a kernel BUG, but a WARNING at the same place:\n\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\n\nbut the root-cause (flag-drop) remains the same.\n\n[akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel]","state":"PUBLISHED","assigner":"Linux","published_at":"2025-10-28 12:15:37","updated_at":"2026-07-30 06:24:07"},"problem_types":["NVD-CWE-noinfo"],"metrics":[{"version":"3.1","source":"nvd@nist.gov","type":"Primary","score":"5.5","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":5.5,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"}},{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60","name":"https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71","name":"https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd","name":"https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18","name":"https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe","name":"https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/788e5385d0ff69cdba1cabccb9dab8d9647b9239","name":"https://git.kernel.org/stable/c/788e5385d0ff69cdba1cabccb9dab8d9647b9239","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93","name":"https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693","name":"https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2025-40040","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-40040","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 788e5385d0ff69cdba1cabccb9dab8d9647b9239 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 b69f19244c2b6475c8a6eb72f0fb0d53509e48cd git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 92b82e232b8d8b116ac6e57aeae7a6033db92c60 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 ac50c6e0a8f91a02b681af81abb2362fbb67cc18 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 76385629f45740b7888f8fcd83bde955b10f61fe git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 63c17fb8e5a46a16e10e82005748837fd11a2024 f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4.6","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 4.6 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.4.302 5.4.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.10.247 5.10.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.197 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.158 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.114 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.55 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.17.3 6.17.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[{"cve_year":"2025","cve_id":"40040","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"o","cpe4":"linux","cpe5":"linux_kernel","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["include/linux/mm.h","rust/bindings/bindings_helper.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"788e5385d0ff69cdba1cabccb9dab8d9647b9239","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"b69f19244c2b6475c8a6eb72f0fb0d53509e48cd","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"92b82e232b8d8b116ac6e57aeae7a6033db92c60","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"ac50c6e0a8f91a02b681af81abb2362fbb67cc18","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"76385629f45740b7888f8fcd83bde955b10f61fe","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"},{"lessThan":"f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93","status":"affected","version":"63c17fb8e5a46a16e10e82005748837fd11a2024","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["include/linux/mm.h","rust/bindings/bindings_helper.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"4.6"},{"lessThan":"4.6","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.4.*","status":"unaffected","version":"5.4.302","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.247","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.197","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.158","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.114","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.55","versionType":"semver"},{"lessThanOrEqual":"6.17.*","status":"unaffected","version":"6.17.3","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"6.18","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.4.302","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.247","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.197","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.158","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.114","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.55","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.17.3","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18","versionStartIncluding":"4.6","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/ksm: fix flag-dropping behavior in ksm_madvise\n\nsyzkaller discovered the following crash: (kernel BUG)\n\n[   44.607039] ------------[ cut here ]------------\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\n\n<snip other registers, drop unreliable trace>\n\n[   44.617726] Call Trace:\n[   44.617926]  <TASK>\n[   44.619284]  userfaultfd_release+0xef/0x1b0\n[   44.620976]  __fput+0x3f9/0xb60\n[   44.621240]  fput_close_sync+0x110/0x210\n[   44.622222]  __x64_sys_close+0x8f/0x120\n[   44.622530]  do_syscall_64+0x5b/0x2f0\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[   44.623244] RIP: 0033:0x7f365bb3f227\n\nKernel panics because it detects UFFD inconsistency during\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\nto vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags.\n\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\nit accidentally clears all flags stored in the upper 32 bits of\nvma->vm_flags.\n\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\nint are 32-bit wide.  This setup causes the following mishap during the &=\n~VM_MERGEABLE assignment.\n\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. \nAfter ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then\npromoted to unsigned long before the & operation.  This promotion fills\nupper 32 bits with leading 0s, as we're doing unsigned conversion (and\neven for a signed conversion, this wouldn't help as the leading bit is 0).\n& operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff\ninstead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears\nthe upper 32-bits of its value.\n\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\nBIT() macro.\n\nNote: other VM_* flags are not affected: This only happens to the\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\nand after ~ operation, they end up with leading 1 and are thus converted\nto unsigned long with leading 1s.\n\nNote 2:\nAfter commit 31defc3b01d9 (\"userfaultfd: remove (VM_)BUG_ON()s\"), this is\nno longer a kernel BUG, but a WARNING at the same place:\n\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\n\nbut the root-cause (flag-drop) remains the same.\n\n[akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel]"}],"metrics":[{"cvssV3_1":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"providerMetadata":{"dateUpdated":"2026-07-30T06:00:04.809Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71"},{"url":"https://git.kernel.org/stable/c/788e5385d0ff69cdba1cabccb9dab8d9647b9239"},{"url":"https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd"},{"url":"https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693"},{"url":"https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60"},{"url":"https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18"},{"url":"https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe"},{"url":"https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93"}],"title":"mm/ksm: fix flag-dropping behavior in ksm_madvise","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2025-40040","datePublished":"2025-10-28T11:48:20.395Z","dateReserved":"2025-04-16T07:20:57.154Z","dateUpdated":"2026-07-30T06:00:04.809Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2025-10-28 12:15:37","lastModifiedDate":"2026-07-30 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fix flag-dropping behavior in ksm_madvise","CVE":"CVE-2025-40040","Year":"2025"},"notes":[{"CveYear":"2025","CveId":"40040","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/ksm: fix flag-dropping behavior in ksm_madvise\n\nsyzkaller discovered the following crash: (kernel BUG)\n\n[   44.607039] ------------[ cut here ]------------\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\n\n<snip other registers, drop unreliable trace>\n\n[   44.617726] Call Trace:\n[   44.617926]  <TASK>\n[   44.619284]  userfaultfd_release+0xef/0x1b0\n[   44.620976]  __fput+0x3f9/0xb60\n[   44.621240]  fput_close_sync+0x110/0x210\n[   44.622222]  __x64_sys_close+0x8f/0x120\n[   44.622530]  do_syscall_64+0x5b/0x2f0\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[   44.623244] RIP: 0033:0x7f365bb3f227\n\nKernel panics because it detects UFFD inconsistency during\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\nto vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags.\n\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\nit accidentally clears all flags stored in the upper 32 bits of\nvma->vm_flags.\n\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\nint are 32-bit wide.  This setup causes the following mishap during the &=\n~VM_MERGEABLE assignment.\n\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. \nAfter ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then\npromoted to unsigned long before the & operation.  This promotion fills\nupper 32 bits with leading 0s, as we're doing unsigned conversion (and\neven for a signed conversion, this wouldn't help as the leading bit is 0).\n& operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff\ninstead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears\nthe upper 32-bits of its value.\n\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\nBIT() macro.\n\nNote: other VM_* flags are not affected: This only happens to the\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\nand after ~ operation, they end up with leading 1 and are thus converted\nto unsigned long with leading 1s.\n\nNote 2:\nAfter commit 31defc3b01d9 (\"userfaultfd: remove (VM_)BUG_ON()s\"), this is\nno longer a kernel BUG, but a WARNING at the same place:\n\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\n\nbut the root-cause (flag-drop) remains the same.\n\n[akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel]","Type":"Description","Title":"mm/ksm: fix flag-dropping behavior in ksm_madvise"}]}}}