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CVE-2021-29657

Status Candidate

Overview

arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.

Related Files

KVM nested_svm_vmrun Double Fetch
Posted Jun 30, 2021
Authored by Google Security Research, Felix Wilhelm

A KVM guest on AMD can launch a L2 guest without the Intercept VMRUN control bit by exploiting a TOCTOU vulnerability in nested_svm_vmrun. Executing vmrun from the L2 guest, will then trigger a second call to nested_svm_vmrun and corrupt svm->nested.hsave with data copied out of the L2 vmcb. For kernel versions that include the commit "2fcf4876: KVM: nSVM: implement on demand allocation of the nested state" (>=5.10), the guest can free the MSR permission bit in svm->nested.msrpm, while it's still in use and gain unrestricted access to host MSRs.

tags | exploit, kernel
advisories | CVE-2021-29657
SHA-256 | d7d8893258c173535d6129f18da5eea5e87415de98e53b981565c55447d30da4
Ubuntu Security Notice USN-4948-1
Posted May 12, 2021
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 4948-1 - Ryota Shiga discovered that the eBPF implementation in the Linux kernel did not properly verify that a BPF program only reserved as much memory for a ring buffer as was allocated. A local attacker could use this to cause a denial of service or execute arbitrary code. Manfred Paul discovered that the eBPF implementation in the Linux kernel did not properly track bounds on bitwise operations. A local attacker could use this to cause a denial of service or execute arbitrary code. Various other issues were also addressed.

tags | advisory, denial of service, arbitrary, kernel, local
systems | linux, ubuntu
advisories | CVE-2020-25670, CVE-2021-28688, CVE-2021-28951, CVE-2021-28952, CVE-2021-28964, CVE-2021-28971, CVE-2021-28972, CVE-2021-29264, CVE-2021-29266, CVE-2021-29646, CVE-2021-29647, CVE-2021-29649, CVE-2021-29650, CVE-2021-29657, CVE-2021-31916, CVE-2021-3483, CVE-2021-3489, CVE-2021-3490, CVE-2021-3491
SHA-256 | 957eb73e74d19d4c62c7116de0b476cf551491d297e087fb9602eff91b7ee985
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