{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2021-47094", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-02-29T22:33:44.300Z", "datePublished": "2024-03-04T18:10:45.240Z", "dateUpdated": "2026-08-05T08:45:57.100Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:45:57.100Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don't advance iterator after restart due to yielding\n\nAfter dropping mmu_lock in the TDP MMU, restart the iterator during\ntdp_iter_next() and do not advance the iterator. Advancing the iterator\nresults in skipping the top-level SPTE and all its children, which is\nfatal if any of the skipped SPTEs were not visited before yielding.\n\nWhen zapping all SPTEs, i.e. when min_level == root_level, restarting the\niter and then invoking tdp_iter_next() is always fatal if the current gfn\nhas as a valid SPTE, as advancing the iterator results in try_step_side()\nskipping the current gfn, which wasn't visited before yielding.\n\nSprinkle WARNs on iter->yielded being true in various helpers that are\noften used in conjunction with yielding, and tag the helper with\n__must_check to reduce the probabily of improper usage.\n\nFailing to zap a top-level SPTE manifests in one of two ways. If a valid\nSPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),\nthe shadow page will be leaked and KVM will WARN accordingly.\n\n WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]\n RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]\n Call Trace:\n \n kvm_arch_destroy_vm+0x130/0x1b0 [kvm]\n kvm_destroy_vm+0x162/0x2a0 [kvm]\n kvm_vcpu_release+0x34/0x60 [kvm]\n __fput+0x82/0x240\n task_work_run+0x5c/0x90\n do_exit+0x364/0xa10\n ? futex_unqueue+0x38/0x60\n do_group_exit+0x33/0xa0\n get_signal+0x155/0x850\n arch_do_signal_or_restart+0xed/0x750\n exit_to_user_mode_prepare+0xc5/0x120\n syscall_exit_to_user_mode+0x1d/0x40\n do_syscall_64+0x48/0xc0\n entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nIf kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by\nkvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of\nmarking a struct page as dirty/accessed after it has been put back on the\nfree list. This directly triggers a WARN due to encountering a page with\npage_count() == 0, but it can also lead to data corruption and additional\nerrors in the kernel.\n\n WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171\n RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]\n Call Trace:\n \n kvm_set_pfn_dirty+0x120/0x1d0 [kvm]\n __handle_changed_spte+0x92e/0xca0 [kvm]\n __handle_changed_spte+0x63c/0xca0 [kvm]\n __handle_changed_spte+0x63c/0xca0 [kvm]\n __handle_changed_spte+0x63c/0xca0 [kvm]\n zap_gfn_range+0x549/0x620 [kvm]\n kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]\n mmu_free_root_page+0x219/0x2c0 [kvm]\n kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]\n kvm_mmu_unload+0x1c/0xa0 [kvm]\n kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]\n kvm_put_kvm+0x3b1/0x8b0 [kvm]\n kvm_vcpu_release+0x4e/0x70 [kvm]\n __fput+0x1f7/0x8c0\n task_work_run+0xf8/0x1a0\n do_exit+0x97b/0x2230\n do_group_exit+0xda/0x2a0\n get_signal+0x3be/0x1e50\n arch_do_signal_or_restart+0x244/0x17f0\n exit_to_user_mode_prepare+0xcb/0x120\n syscall_exit_to_user_mode+0x1d/0x40\n do_syscall_64+0x4d/0x90\n entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nNote, the underlying bug existed even before commit 1af4a96025b3 (\"KVM:\nx86/mmu: Yield in TDU MMU iter even if no SPTES changed\") moved calls to\ntdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still\nincorrectly advance past a top-level entry when yielding on a lower-level\nentry. But with respect to leaking shadow pages, the bug was introduced\nby yielding before processing the current gfn.\n\nAlternatively, tdp_mmu_iter_cond_resched() could simply fall through, or\ncallers could jump to their \"retry\" label. The downside of that approach\nis that tdp_mmu_iter_cond_resched() _must_ be called before anything else\nin the loop, and there's no easy way to enfornce that requirement.\n\nIdeally, KVM would handling the cond_resched() fully within the iterator\nmacro (the code is actually quite clean) and avoid this entire class of\nbugs, but that is extremely difficult do wh\n---truncated---" } ], "metrics": [ { "cvssV3_1": { "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" }, "scenarios": [ { "lang": "en", "value": "AV:L - The bug is reached via host KVM ioctls on /dev/kvm (create VM, populate TDP SPTEs, then zap on memslot changes or VM destroy), not via network packets or guest-only operations.\nAC:L - An attacker who creates a large guest memory map can reliably force tdp_mmu_iter_cond_resched() yields (need_resched/lock contention), and once a yield occurs during zap-all the skipped top-level SPTE is deterministic.\nPR:L - Opening /dev/kvm and creating VMs requires only local access granted by device permissions (typically kvm-group membership); the kernel path does not require CAP_SYS_ADMIN or real root.\nUI:N - Exploitation needs no victim action beyond the attacker’s own KVM VM create/map/destroy (or memslot zap) sequence.\nS:U - This is host-userspace-to-host-kernel memory corruption in KVM’s TDP MMU, not a guest-to-host escape across the VM isolation boundary.\nC:H - The flawed zap path can UAF freed struct pages (mark dirty/accessed after return to the freelist), which per UAF guidance enables arbitrary host memory disclosure primitives.\nI:H - The commit explicitly reports use-after-free leading to host data corruption when leftover SPTEs are later zapped against already-freed pages, enabling integrity compromise and further write primitives.\nA:H - The bug triggers kernel WARNs/oops paths and use-after-free behavior that can crash or hang the host during VM teardown or zap." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/mmu/tdp_iter.c", "arch/x86/kvm/mmu/tdp_iter.h", "arch/x86/kvm/mmu/tdp_mmu.c" ], "versions": [ { "version": "faaf05b00aecdb347ffd1d763d024394ec0329f8", "lessThan": "d884eefd75cc54887bc2e9e724207443525dfb2c", "status": "affected", "versionType": "git" }, { "version": "faaf05b00aecdb347ffd1d763d024394ec0329f8", "lessThan": "3a0f64de479cae75effb630a2e0a237ca0d0623c", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/mmu/tdp_iter.c", "arch/x86/kvm/mmu/tdp_iter.h", "arch/x86/kvm/mmu/tdp_mmu.c" ], "versions": [ { "version": "5.10", "status": "affected" }, { "version": "0", "lessThan": "5.10", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.12", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.16", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.10", "versionEndExcluding": "5.15.12" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.10", "versionEndExcluding": "5.16" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c" }, { "url": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c" } ], "title": "KVM: x86/mmu: Don't advance iterator after restart due to yielding", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "problemTypes": [ { "descriptions": [ { "type": "CWE", "lang": "en", "description": "CWE-noinfo Not enough information" } ] } ], "metrics": [ { "cvssV3_1": { "scope": "UNCHANGED", "version": "3.1", "baseScore": 7.1, "attackVector": "LOCAL", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH" } }, { "other": { "type": "ssvc", "content": { "timestamp": "2024-03-06T15:25:43.452334Z", "id": "CVE-2021-47094", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-11-07T17:31:11.450Z" } }, { "providerMetadata": { "orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T05:24:39.844Z" }, "title": "CVE Program Container", "references": [ { "url": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c", "tags": [ "x_transferred" ] }, { "url": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c", "tags": [ "x_transferred" ] } ] } ] } }