CVE-2020-8834 Information

Description

KVM in the Linux kernel on Power8 processors has a conflicting use of HSTATE_HOST_R1 to store r1 state in kvmppc_hv_entry plus in kvmppc_saverestore_tm leading to a stack corruption. Because of this an attacker with the ability run code in kernel space of a guest VM can cause the host kernel to panic. There were two commits that according to the reporter introduced the vulnerability: f024ee098476 (\KVM: PPC: Book3S HV: Pull out TM state save/restore into separate procedures) 87a11bb6a7f7 (\KVM: PPC: Book3S HV: Work around XER[SO] bug in fake suspend mode) The former landed in 4.8 the latter in 4.17. This was fixed without realizing the impact in 4.18 with the following three commits though it’s believed the first is the only strictly necessary commit: 6f597c6b63b6 (\KVM: PPC: Book3S PR: Add guest MSR parameter for kvmppc_save_tm()/kvmppc_restore_tm()) 7b0e827c6970 (\KVM: PPC: Book3S HV: Factor fake-suspend handling out of kvmppc_save/restore_tm) 009c872a8bc4 (\KVM: PPC: Book3S PR: Move kvmppc_save_tm/kvmppc_restore_tm to separate file)

CVSS Vector

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

Reference

http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00035.html https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1867717 https://usn.ubuntu.com/4318-1/ https://usn.ubuntu.com/usn/usn-4318-1 https://www.openwall.com/lists/oss-security/2020/04/06/2

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

CHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

6.5