CVE-2021-47092
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: VMX: Always clear vmx->fail on emulation_required
Revert a relatively recent change that set vmx->fail if the vCPU is in L2
and emulation_required is true, as that behavior is completely bogus.
Setting vmx->fail and synthesizing a VM-Exit is contradictory and wrong:
(a) it's impossible to have both a VM-Fail and VM-Exit
(b) vmcs.EXIT_REASON is not modified on VM-Fail
(c) emulation_required refers to guest state and guest state checks are
always VM-Exits, not VM-Fails.
For KVM specifically, emulation_required is handled before nested exits
in __vmx_handle_exit(), thus setting vmx->fail has no immediate effect,
i.e. KVM calls into handle_invalid_guest_state() and vmx->fail is ignored.
Setting vmx->fail can ultimately result in a WARN in nested_vmx_vmexit()
firing when tearing down the VM as KVM never expects vmx->fail to be set
when L2 is active, KVM always reflects those errors into L1.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 21158 at arch/x86/kvm/vmx/nested.c:4548
nested_vmx_vmexit+0x16bd/0x17e0
arch/x86/kvm/vmx/nested.c:4547
Modules linked in:
CPU: 0 PID: 21158 Comm: syz-executor.1 Not tainted 5.16.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547
Code: <0f> 0b e9 2e f8 ff ff e8 57 b3 5d 00 0f 0b e9 00 f1 ff ff 89 e9 80
Call Trace:
vmx_leave_nested arch/x86/kvm/vmx/nested.c:6220 [inline]
nested_vmx_free_vcpu+0x83/0xc0 arch/x86/kvm/vmx/nested.c:330
vmx_free_vcpu+0x11f/0x2a0 arch/x86/kvm/vmx/vmx.c:6799
kvm_arch_vcpu_destroy+0x6b/0x240 arch/x86/kvm/x86.c:10989
kvm_vcpu_destroy+0x29/0x90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:441
kvm_free_vcpus arch/x86/kvm/x86.c:11426 [inline]
kvm_arch_destroy_vm+0x3ef/0x6b0 arch/x86/kvm/x86.c:11545
kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1189 [inline]
kvm_put_kvm+0x751/0xe40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1220
kvm_vcpu_release+0x53/0x60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3489
__fput+0x3fc/0x870 fs/file_table.c:280
task_work_run+0x146/0x1c0 kernel/task_work.c:164
exit_task_work include/linux/task_work.h:32 [inline]
do_exit+0x705/0x24f0 kernel/exit.c:832
do_group_exit+0x168/0x2d0 kernel/exit.c:929
get_signal+0x1740/0x2120 kernel/signal.c:2852
arch_do_signal_or_restart+0x9c/0x730 arch/x86/kernel/signal.c:868
handle_signal_work kernel/entry/common.c:148 [inline]
exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
exit_to_user_mode_prepare+0x191/0x220 kernel/entry/common.c:207
__syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300
do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x44/0xae
References
Impacted products
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"cveId": "CVE-2021-47092",
"datePublished": "2024-03-04T18:10:40.037Z",
"dateReserved": "2024-02-29T22:33:44.300Z",
"dateUpdated": "2024-12-19T07:35:04.267Z",
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"nvd": "{\"cve\":{\"id\":\"CVE-2021-47092\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2024-03-04T18:15:07.723\",\"lastModified\":\"2024-11-21T06:35:22.863\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: VMX: Always clear vmx-\u003efail on emulation_required\\n\\nRevert a relatively recent change that set vmx-\u003efail if the vCPU is in L2\\nand emulation_required is true, as that behavior is completely bogus.\\nSetting vmx-\u003efail and synthesizing a VM-Exit is contradictory and wrong:\\n\\n (a) it\u0027s impossible to have both a VM-Fail and VM-Exit\\n (b) vmcs.EXIT_REASON is not modified on VM-Fail\\n (c) emulation_required refers to guest state and guest state checks are\\n always VM-Exits, not VM-Fails.\\n\\nFor KVM specifically, emulation_required is handled before nested exits\\nin __vmx_handle_exit(), thus setting vmx-\u003efail has no immediate effect,\\ni.e. KVM calls into handle_invalid_guest_state() and vmx-\u003efail is ignored.\\nSetting vmx-\u003efail can ultimately result in a WARN in nested_vmx_vmexit()\\nfiring when tearing down the VM as KVM never expects vmx-\u003efail to be set\\nwhen L2 is active, KVM always reflects those errors into L1.\\n\\n ------------[ cut here ]------------\\n WARNING: CPU: 0 PID: 21158 at arch/x86/kvm/vmx/nested.c:4548\\n nested_vmx_vmexit+0x16bd/0x17e0\\n arch/x86/kvm/vmx/nested.c:4547\\n Modules linked in:\\n CPU: 0 PID: 21158 Comm: syz-executor.1 Not tainted 5.16.0-rc3-syzkaller #0\\n Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011\\n RIP: 0010:nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547\\n Code: \u003c0f\u003e 0b e9 2e f8 ff ff e8 57 b3 5d 00 0f 0b e9 00 f1 ff ff 89 e9 80\\n Call Trace:\\n vmx_leave_nested arch/x86/kvm/vmx/nested.c:6220 [inline]\\n nested_vmx_free_vcpu+0x83/0xc0 arch/x86/kvm/vmx/nested.c:330\\n vmx_free_vcpu+0x11f/0x2a0 arch/x86/kvm/vmx/vmx.c:6799\\n kvm_arch_vcpu_destroy+0x6b/0x240 arch/x86/kvm/x86.c:10989\\n kvm_vcpu_destroy+0x29/0x90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:441\\n kvm_free_vcpus arch/x86/kvm/x86.c:11426 [inline]\\n kvm_arch_destroy_vm+0x3ef/0x6b0 arch/x86/kvm/x86.c:11545\\n kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1189 [inline]\\n kvm_put_kvm+0x751/0xe40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1220\\n kvm_vcpu_release+0x53/0x60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3489\\n __fput+0x3fc/0x870 fs/file_table.c:280\\n task_work_run+0x146/0x1c0 kernel/task_work.c:164\\n exit_task_work include/linux/task_work.h:32 [inline]\\n do_exit+0x705/0x24f0 kernel/exit.c:832\\n do_group_exit+0x168/0x2d0 kernel/exit.c:929\\n get_signal+0x1740/0x2120 kernel/signal.c:2852\\n arch_do_signal_or_restart+0x9c/0x730 arch/x86/kernel/signal.c:868\\n handle_signal_work kernel/entry/common.c:148 [inline]\\n exit_to_user_mode_loop kernel/entry/common.c:172 [inline]\\n exit_to_user_mode_prepare+0x191/0x220 kernel/entry/common.c:207\\n __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]\\n syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300\\n do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86\\n entry_SYSCALL_64_after_hwframe+0x44/0xae\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: KVM: VMX: borre siempre vmx-\u0026gt;fail en emulation_required Revierta un cambio relativamente reciente que establece vmx-\u0026gt;fail si la vCPU est\u00e1 en L2 y emulation_required es verdadero, ya que ese comportamiento es completamente falso. Configurar vmx-\u0026gt;fail y sintetizar una VM-Exit es contradictorio y incorrecto: (a) es imposible tener VM-Fail y VM-Exit (b) vmcs.EXIT_REASON no se modifica en VM-Fail (c) emulation_required se refiere al estado invitado y las comprobaciones del estado invitado son siempre salidas de VM, no fallas de VM. Para KVM espec\u00edficamente, emulation_required se maneja antes de las salidas anidadas en __vmx_handle_exit(), por lo que configurar vmx-\u0026gt;fail no tiene un efecto inmediato, es decir, las llamadas de KVM a handle_invalid_guest_state() y vmx-\u0026gt;fail se ignoran. Configurar vmx-\u0026gt;fail puede, en \u00faltima instancia, generar una ADVERTENCIA en nested_vmx_vmexit() al desactivar la VM, ya que KVM nunca espera que vmx-\u0026gt;fail se configure cuando L2 est\u00e1 activo, KVM siempre refleja esos errores en L1. ------------[ cortar aqu\u00ed ]------------ ADVERTENCIA: CPU: 0 PID: 21158 en arch/x86/kvm/vmx/nested.c:4548 nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547 M\u00f3dulos vinculados en: CPU: 0 PID: 21158 Comm: syz-executor.1 No contaminado 5.16.0-rc3-syzkaller #0 Nombre de hardware: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547 C\u00f3digo: \u0026lt;0f\u0026gt; 0b e9 2e f8 ff ff e8 57 b3 5d 00 0f 0b e9 00 f1 ff ff 89 e9 80 Seguimiento de llamadas: vmx_leave_nested arch/x86/kvm/vmx/nested.c:6220 [en l\u00ednea] nested_vmx_free_vcpu+0x83/0xc0 arch/x86/kvm/vmx/nested.c: 330 vmx_free_vcpu+0x11f/0x2a0 arch/x86/kvm/vmx/vmx.c:6799 kvm_arch_vcpu_destroy+0x6b/0x240 arch/x86/kvm/x86.c:10989 kvm_vcpu_destroy+0x29/0x90 arch/x86/kvm/.. /. ./../virt/kvm/kvm_main.c:441 kvm_free_vcpus arch/x86/kvm/x86.c:11426 [en l\u00ednea] kvm_arch_destroy_vm+0x3ef/0x6b0 arch/x86/kvm/x86.c:11545 kvm_destroy_vm arch/x86/ kvm/../../../virt/kvm/kvm_main.c:1189 [en l\u00ednea] kvm_put_kvm+0x751/0xe40 arch/x86/kvm/../../../virt/kvm/kvm_main.c :1220 kvm_vcpu_release+0x53/0x60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3489 __fput+0x3fc/0x870 fs/file_table.c:280 task_work_run+0x146/0x1c0 kernel/ task_work.c:164 exit_task_work include/linux/task_work.h:32 [en l\u00ednea] do_exit+0x705/0x24f0 kernel/exit.c:832 do_group_exit+0x168/0x2d0 kernel/exit.c:929 get_signal+0x1740/0x2120 kernel/se\u00f1al .c:2852 arch_do_signal_or_restart+0x9c/0x730 arch/x86/kernel/signal.c:868 handle_signal_work kernel/entry/common.c:148 [en l\u00ednea] exit_to_user_mode_loop kernel/entry/common.c:172 [en l\u00ednea] exit_to_user_mode_prepare+0x191/ 0x220 kernel/entry/common.c:207 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [en l\u00ednea] syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300 do_syscall_64+0x53/0xd0 arch/x86/entry/common. c:86 entrada_SYSCALL_64_after_hwframe+0x44/0xae\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/a80dfc025924024d2c61a4c1b8ef62b2fce76a04\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e4e4e7cb229821cd215031abc47efdab5486a67c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a80dfc025924024d2c61a4c1b8ef62b2fce76a04\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"https://git.kernel.org/stable/c/e4e4e7cb229821cd215031abc47efdab5486a67c\",\"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.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- 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.