{ "data_version": "4.0", "data_type": "CVE", "data_format": "MITRE", "CVE_data_meta": { "ID": "CVE-2021-47094", "ASSIGNER": "cve@kernel.org", "STATE": "PUBLIC" }, "description": { "description_data": [ { "lang": "eng", "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---" } ] }, "problemtype": { "problemtype_data": [ { "description": [ { "lang": "eng", "value": "n/a" } ] } ] }, "affects": { "vendor": { "vendor_data": [ { "vendor_name": "Linux", "product": { "product_data": [ { "product_name": "Linux", "version": { "version_data": [ { "version_affected": "<", "version_name": "faaf05b00aec", "version_value": "d884eefd75cc" }, { "version_value": "not down converted", "x_cve_json_5_version_data": { "versions": [ { "version": "5.10", "status": "affected" }, { "version": "0", "lessThan": "5.10", "status": "unaffected", "versionType": "custom" }, { "version": "5.15.12", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.16", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ], "defaultStatus": "affected" } } ] } } ] } } ] } }, "references": { "reference_data": [ { "url": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c" }, { "url": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c" } ] }, "generator": { "engine": "bippy-a5840b7849dd" } }