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CVE-2021-46978

HIGH
Published 2024-02-28T08:13:09.106Z
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CVSS Score

V3.1
7.8
/10
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Base Score Metrics
Exploitability: N/A Impact: N/A

EPSS Score

v2025.03.14
0.000
probability
of exploitation in the wild

There is a 0.0% chance that this vulnerability will be exploited in the wild within the next 30 days.

Updated: 2025-06-25
Exploit Probability
Percentile: 0.144
Higher than 14.4% of all CVEs

Attack Vector Metrics

Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED

Impact Metrics

Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH

Description

In the Linux kernel, the following vulnerability has been resolved:

KVM: nVMX: Always make an attempt to map eVMCS after migration

When enlightened VMCS is in use and nested state is migrated with
vmx_get_nested_state()/vmx_set_nested_state() KVM can't map evmcs
page right away: evmcs gpa is not 'struct kvm_vmx_nested_state_hdr'
and we can't read it from VP assist page because userspace may decide
to restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state
(and QEMU, for example, does exactly that). To make sure eVMCS is
mapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES
request.

Commit f2c7ef3ba955 ("KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES
on nested vmexit") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to
nested_vmx_vmexit() to make sure MSR permission bitmap is not switched
when an immediate exit from L2 to L1 happens right after migration (caused
by a pending event, for example). Unfortunately, in the exact same
situation we still need to have eVMCS mapped so
nested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.

As a band-aid, restore nested_get_evmcs_page() when clearing
KVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far
from being ideal as we can't easily propagate possible failures and even if
we could, this is most likely already too late to do so. The whole
'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration
seems to be fragile as we diverge too much from the 'native' path when
vmptr loading happens on vmx_set_nested_state().

Available Exploits

No exploits available for this CVE.

Related News

No news articles found for this CVE.

Affected Products

Linux

Linux

Affected Versions:

0faceb7d6dda6f370ff1fa0464d7180f7e5cb417 f2c7ef3ba9556d62a7e2bb23b563c6510007d55c f2c7ef3ba9556d62a7e2bb23b563c6510007d55c f2c7ef3ba9556d62a7e2bb23b563c6510007d55c
Linux

Linux

Affected Versions:

5.11 0 5.10.38 5.11.22 5.12.5 5.13
linux

linux_kernel

Affected Versions:

0faceb7d6dda f2c7ef3ba955 f2c7ef3ba955 f2c7ef3ba955 5.11 0 5.10.38 5.12.5 5.13

GitHub Security Advisories

Community-driven vulnerability intelligence from GitHub

⚠ Unreviewed HIGH

GHSA-frh6-wfp2-xc99

Advisory Details

In the Linux kernel, the following vulnerability has been resolved: KVM: nVMX: Always make an attempt to map eVMCS after migration When enlightened VMCS is in use and nested state is migrated with vmx_get_nested_state()/vmx_set_nested_state() KVM can't map evmcs page right away: evmcs gpa is not 'struct kvm_vmx_nested_state_hdr' and we can't read it from VP assist page because userspace may decide to restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state (and QEMU, for example, does exactly that). To make sure eVMCS is mapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES request. Commit f2c7ef3ba955 ("KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to nested_vmx_vmexit() to make sure MSR permission bitmap is not switched when an immediate exit from L2 to L1 happens right after migration (caused by a pending event, for example). Unfortunately, in the exact same situation we still need to have eVMCS mapped so nested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS. As a band-aid, restore nested_get_evmcs_page() when clearing KVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far from being ideal as we can't easily propagate possible failures and even if we could, this is most likely already too late to do so. The whole 'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration seems to be fragile as we diverge too much from the 'native' path when vmptr loading happens on vmx_set_nested_state().

CVSS Scoring

CVSS Score

7.5

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

References

ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2021-46978
WEB https://git.kernel.org/stable/c/200a45649ab7361bc80c70aebf7165b64f9a6c9f
WEB https://git.kernel.org/stable/c/bd0e8455b85b651a4c77de9616e307129b15aaa7
WEB https://git.kernel.org/stable/c/c8bf64e3fb77cc19bad146fbe26651985b117194
WEB https://git.kernel.org/stable/c/f5c7e8425f18fdb9bdb7d13340651d7876890329

Advisory provided by GitHub Security Advisory Database. Published: February 28, 2024, Modified: November 4, 2024

References

https://git.kernel.org/stable/c/c8bf64e3fb77cc19bad146fbe26651985b117194
https://git.kernel.org/stable/c/200a45649ab7361bc80c70aebf7165b64f9a6c9f
https://git.kernel.org/stable/c/bd0e8455b85b651a4c77de9616e307129b15aaa7
https://git.kernel.org/stable/c/f5c7e8425f18fdb9bdb7d13340651d7876890329
Published: 2024-02-28T08:13:09.106Z
Last Modified: 2025-05-04T07:01:32.538Z
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