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ubuntucveUbuntu.comUB:CVE-2020-8834
HistoryApr 06, 2020 - 12:00 a.m.

CVE-2020-8834

2020-04-0600:00:00
ubuntu.com
ubuntu.com
12

6.5 Medium

CVSS3

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

4.9 Medium

CVSS2

Access Vector

LOCAL

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:L/AC:L/Au:N/C:N/I:N/A:C

0.001 Low

EPSS

Percentile

21.5%

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”)

Bugs

Notes

Author Note
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()
OSVersionArchitecturePackageVersionFilename
ubuntu18.04noarchlinux< 4.15.0-96.97UNKNOWN
ubuntu16.04noarchlinux-hwe< 4.15.0-96.97~16.04.1UNKNOWN

6.5 Medium

CVSS3

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

4.9 Medium

CVSS2

Access Vector

LOCAL

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:L/AC:L/Au:N/C:N/I:N/A:C

0.001 Low

EPSS

Percentile

21.5%