CVE-2021-47094
Vulnerability from cvelistv5
Published
2024-03-04 18:10
Modified
2024-12-19 07:35
Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86/mmu: Don't advance iterator after restart due to yielding
After dropping mmu_lock in the TDP MMU, restart the iterator during
tdp_iter_next() and do not advance the iterator. Advancing the iterator
results in skipping the top-level SPTE and all its children, which is
fatal if any of the skipped SPTEs were not visited before yielding.
When zapping all SPTEs, i.e. when min_level == root_level, restarting the
iter and then invoking tdp_iter_next() is always fatal if the current gfn
has as a valid SPTE, as advancing the iterator results in try_step_side()
skipping the current gfn, which wasn't visited before yielding.
Sprinkle WARNs on iter->yielded being true in various helpers that are
often used in conjunction with yielding, and tag the helper with
__must_check to reduce the probabily of improper usage.
Failing to zap a top-level SPTE manifests in one of two ways. If a valid
SPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),
the shadow page will be leaked and KVM will WARN accordingly.
WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]
RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]
Call Trace:
<TASK>
kvm_arch_destroy_vm+0x130/0x1b0 [kvm]
kvm_destroy_vm+0x162/0x2a0 [kvm]
kvm_vcpu_release+0x34/0x60 [kvm]
__fput+0x82/0x240
task_work_run+0x5c/0x90
do_exit+0x364/0xa10
? futex_unqueue+0x38/0x60
do_group_exit+0x33/0xa0
get_signal+0x155/0x850
arch_do_signal_or_restart+0xed/0x750
exit_to_user_mode_prepare+0xc5/0x120
syscall_exit_to_user_mode+0x1d/0x40
do_syscall_64+0x48/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
If kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by
kvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of
marking a struct page as dirty/accessed after it has been put back on the
free list. This directly triggers a WARN due to encountering a page with
page_count() == 0, but it can also lead to data corruption and additional
errors in the kernel.
WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171
RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]
Call Trace:
<TASK>
kvm_set_pfn_dirty+0x120/0x1d0 [kvm]
__handle_changed_spte+0x92e/0xca0 [kvm]
__handle_changed_spte+0x63c/0xca0 [kvm]
__handle_changed_spte+0x63c/0xca0 [kvm]
__handle_changed_spte+0x63c/0xca0 [kvm]
zap_gfn_range+0x549/0x620 [kvm]
kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]
mmu_free_root_page+0x219/0x2c0 [kvm]
kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]
kvm_mmu_unload+0x1c/0xa0 [kvm]
kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]
kvm_put_kvm+0x3b1/0x8b0 [kvm]
kvm_vcpu_release+0x4e/0x70 [kvm]
__fput+0x1f7/0x8c0
task_work_run+0xf8/0x1a0
do_exit+0x97b/0x2230
do_group_exit+0xda/0x2a0
get_signal+0x3be/0x1e50
arch_do_signal_or_restart+0x244/0x17f0
exit_to_user_mode_prepare+0xcb/0x120
syscall_exit_to_user_mode+0x1d/0x40
do_syscall_64+0x4d/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Note, the underlying bug existed even before commit 1af4a96025b3 ("KVM:
x86/mmu: Yield in TDU MMU iter even if no SPTES changed") moved calls to
tdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still
incorrectly advance past a top-level entry when yielding on a lower-level
entry. But with respect to leaking shadow pages, the bug was introduced
by yielding before processing the current gfn.
Alternatively, tdp_mmu_iter_cond_resched() could simply fall through, or
callers could jump to their "retry" label. The downside of that approach
is that tdp_mmu_iter_cond_resched() _must_ be called before anything else
in the loop, and there's no easy way to enfornce that requirement.
Ideally, KVM would handling the cond_resched() fully within the iterator
macro (the code is actually quite clean) and avoid this entire class of
bugs, but that is extremely difficult do wh
---truncated---
References
Impacted products
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"confidentialityImpact": "HIGH",
"integrityImpact": "NONE",
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"scope": "UNCHANGED",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don\u0027t 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\u0027t visited before yielding.\n\nSprinkle WARNs on iter-\u003eyielded 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 \u003cTASK\u003e\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 \u003cTASK\u003e\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\u0027s 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---"
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"title": "KVM: x86/mmu: Don\u0027t advance iterator after restart due to yielding",
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"cveId": "CVE-2021-47094",
"datePublished": "2024-03-04T18:10:45.240Z",
"dateReserved": "2024-02-29T22:33:44.300Z",
"dateUpdated": "2024-12-19T07:35:06.529Z",
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"nvd": "{\"cve\":{\"id\":\"CVE-2021-47094\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2024-03-04T18:15:07.837\",\"lastModified\":\"2024-11-21T06:35:23.090\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: x86/mmu: Don\u0027t 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\u0027t visited before yielding.\\n\\nSprinkle WARNs on iter-\u003eyielded 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 \u003cTASK\u003e\\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 \u003cTASK\u003e\\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\u0027s 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---\"},{\"lang\":\"es\",\"value\":\" In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Don\u0027t advance iterator after restart due to yielding After dropping mmu_lock in the TDP MMU, restart the iterator during tdp_iter_next() and do not advance the iterator. Advancing the iterator results in skipping the top-level SPTE and all its children, which is fatal if any of the skipped SPTEs were not visited before yielding. When zapping all SPTEs, i.e. when min_level == root_level, restarting the iter and then invoking tdp_iter_next() is always fatal if the current gfn has as a valid SPTE, as advancing the iterator results in try_step_side() skipping the current gfn, which wasn\u0027t visited before yielding. Sprinkle WARNs on iter-\u0026gt;yielded being true in various helpers that are often used in conjunction with yielding, and tag the helper with __must_check to reduce the probabily of improper usage. Failing to zap a top-level SPTE manifests in one of two ways. If a valid SPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(), the shadow page will be leaked and KVM will WARN accordingly. WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm] RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm] Call Trace: kvm_arch_destroy_vm+0x130/0x1b0 [kvm] kvm_destroy_vm+0x162/0x2a0 [kvm] kvm_vcpu_release+0x34/0x60 [kvm] __fput+0x82/0x240 task_work_run+0x5c/0x90 do_exit+0x364/0xa10 ? futex_unqueue+0x38/0x60 do_group_exit+0x33/0xa0 get_signal+0x155/0x850 arch_do_signal_or_restart+0xed/0x750 exit_to_user_mode_prepare+0xc5/0x120 syscall_exit_to_user_mode+0x1d/0x40 do_syscall_64+0x48/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae If kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by kvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of marking a struct page as dirty/accessed after it has been put back on the free list. This directly triggers a WARN due to encountering a page with page_count() == 0, but it can also lead to data corruption and additional errors in the kernel. WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171 RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm] Call Trace: kvm_set_pfn_dirty+0x120/0x1d0 [kvm] __handle_changed_spte+0x92e/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] zap_gfn_range+0x549/0x620 [kvm] kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm] mmu_free_root_page+0x219/0x2c0 [kvm] kvm_mmu_free_roots+0x1b4/0x4e0 [kvm] kvm_mmu_unload+0x1c/0xa0 [kvm] kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm] kvm_put_kvm+0x3b1/0x8b0 [kvm] kvm_vcpu_release+0x4e/0x70 [kvm] __fput+0x1f7/0x8c0 task_work_run+0xf8/0x1a0 do_exit+0x97b/0x2230 do_group_exit+0xda/0x2a0 get_signal+0x3be/0x1e50 arch_do_signal_or_restart+0x244/0x17f0 exit_to_user_mode_prepare+0xcb/0x120 syscall_exit_to_user_mode+0x1d/0x40 do_syscall_64+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae Note, the underlying bug existed even before commit 1af4a96025b3 (\\\"KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed\\\") moved calls to tdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still incorrectly advance past a top-level entry when yielding on a lower-level entry. But with respect to leaking shadow pages, the bug was introduced by yielding before processing the current gfn. Alternatively, tdp_mmu_iter_cond_resched() could simply fall through, or callers could jump to their \\\"retry\\\" label. The downside of that approach is that tdp_mmu_iter_cond_resched() _must_ be called before anything else in the loop, and there\u0027s no easy way to enfornce that requirement. Ideally, KVM would handling the cond_resched() fully within the iterator macro (the code is actually quite clean) and avoid this entire class of bugs, but that is extremely difficult do wh\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H\",\"baseScore\":7.1,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":5.2}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"}]}}"
}
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
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- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.