CVE-2020-8834 Linux kernel KVM Power8 conflicting use of HSTATE_HOST_R1
A guest VM attacker can trigger a host kernel panic via a race condition in KVM Power8 transactional memory state handling.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2020-8834?
CVE-2020-8834 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 9 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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_{save,restore}_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")
Which versions are affected by CVE-2020-8834?
It affects 3 products.
Products include Canonical Ubuntu Linux, Linux kernel, Opensuse Leap.
How do I fix CVE-2020-8834?
Apply the vendor's patch.
Is CVE-2020-8834 being exploited?
There is no known exploitation of CVE-2020-8834 in the wild and no public exploit code.
Other vulnerabilities in Canonical Ubuntu Linux
Sources
Also known as DEBIAN-CVE-2020-8834, GHSA-7fx7-755p-qmjj, UBUNTU-CVE-2020-8834.