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CVE-2020-8834

Publication date 6 April 2020

Last updated 24 July 2024

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

6.5 · Medium

Score breakdown

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")

From the Ubuntu Security Team

Gustavo Romero and Paul Mackerras discovered that the KVM implementation in the Linux kernel for PowerPC processors did not properly keep guest state separate from host state. A local attacker in a KVM guest could use this to cause a denial of service (host system crash).

Read the notes from the security team

Status

Package Ubuntu Release Status
linux 19.10 eoan
Not affected
18.04 LTS bionic
Fixed 4.15.0-96.97
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
linux-aws 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
linux-aws-5.0 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-aws-hwe 19.10 eoan Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-azure 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
linux-azure-5.3 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-azure-edge 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-gcp 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-gcp-5.3 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-gcp-edge 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-gke-4.15 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-gke-5.0 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-gke-5.3 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-hwe 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial
Fixed 4.15.0-96.97~16.04.1
14.04 LTS trusty Not in release
linux-hwe-edge 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Ignored
14.04 LTS trusty Not in release
linux-kvm 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-lts-trusty 19.10 eoan Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-lts-xenial 19.10 eoan Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial Not in release
14.04 LTS trusty
Not affected
linux-oem 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-oem-5.4 19.10 eoan Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-oem-osp1 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-oracle 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-oracle-5.0 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-oracle-5.3 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-raspi2 19.10 eoan
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
linux-raspi2-5.3 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release
linux-snapdragon 19.10 eoan Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release

Notes

sbeattie

appears to only affect Power8 hardware and not Power9, possibly because transaction memory in Power9 needs a software assist to function. from reporter, introduced in f024ee098476 and exacerbated by 87a11bb6a7f7.

sbeattie

Addressed by: 7b0e827c6970e8ca77c60ae87592204c39e41245 KVM: PPC: Book3S HV: Factor fake-suspend handling out of kvmppc_save/restore_tm 009c872a8bc4d38f487a9bd62423d019e4322517 KVM: PPC: Book3S PR: Move kvmppc_save_tm/kvmppc_restore_tm to separate file 6f597c6b63b6f3675914b5ec8fcd008a58678650 KVM: PPC: Book3S PR: Add guest MSR parameter for kvmppc_save_tm()/kvmppc_restore_tm()

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package Patch details
linux

Severity score breakdown

Parameter Value
Base score 6.5 · Medium
Attack vector Local
Attack complexity Low
Privileges required Low
User interaction None
Scope Changed
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

References

Related Ubuntu Security Notices (USN)

    • USN-4318-1
    • Linux kernel vulnerabilities
    • 6 April 2020

Other references