cbcvebase.
CVE-2021-46978
published 2024-02-28

CVE-2021-46978: 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…

PriorityP337high7.8CVSS 3.1
AVLACLPRLUINSUCHIHAH
EPSS
0.24%
15.4th percentile
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().

Affected

15 ranges
VendorProductVersion rangeFixed in
debianlinux< linux 5.10.38-1 (bookworm)linux 5.10.38-1 (bookworm)
linuxlinux——
linuxlinux>= 0faceb7d6dda6f370ff1fa0464d7180f7e5cb417 < c8bf64e3fb77cc19bad146fbe26651985b117194c8bf64e3fb77cc19bad146fbe26651985b117194
linuxlinux>= 5.10.13 < 5.10.385.10.38
linuxlinux>= f2c7ef3ba9556d62a7e2bb23b563c6510007d55c < 200a45649ab7361bc80c70aebf7165b64f9a6c9f200a45649ab7361bc80c70aebf7165b64f9a6c9f
linuxlinux>= f2c7ef3ba9556d62a7e2bb23b563c6510007d55c < bd0e8455b85b651a4c77de9616e307129b15aaa7bd0e8455b85b651a4c77de9616e307129b15aaa7
linuxlinux>= f2c7ef3ba9556d62a7e2bb23b563c6510007d55c < f5c7e8425f18fdb9bdb7d13340651d7876890329f5c7e8425f18fdb9bdb7d13340651d7876890329
linuxlinux_kernel——
linuxlinux_kernel>= 0 < 5.10.38-15.10.38-1
linuxlinux_kernel>= 0 < 5.10.38-15.10.38-1
linuxlinux_kernel>= 0 < 5.10.38-15.10.38-1
linuxlinux_kernel>= 0 < 5.10.38-15.10.38-1
linuxlinux_kernel>= 5.10.13 < 5.10.385.10.38
linuxlinux_kernel>= 5.11 < 5.11.225.11.22
linuxlinux_kernel>= 5.12 < 5.12.55.12.5

CVSS provenance

nvdv3.17.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
osv7.8HIGH
vendor_debian7.8HIGH
vendor_redhat7.8HIGH
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