CVE-2020-8834 Linux kernel KVM Power8 conflicting use of HSTATE_HOST_R1

2020-04-0600:00:00

CWE-368

canonical

www.cve.org

CVSS3

6.5

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

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

AI Score

6.8

Confidence

High

EPSS

0.001

Percentile

22.7%

JSON

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”)

CNA Affected

[
  {
    "platforms": [
      "PPC Power8"
    ],
    "product": "Linux kernel",
    "vendor": "Linux kernel",
    "versions": [
      {
        "lessThan": "unspecified",
        "status": "affected",
        "version": "4.8",
        "versionType": "custom"
      },
      {
        "lessThan": "4.18",
        "status": "affected",
        "version": "unspecified",
        "versionType": "custom"
      }
    ]
  }
]