Lucene search

K
osvGoogleOSV:GHSA-JQ35-85CJ-FJ4P
HistoryOct 30, 2023 - 3:25 p.m.

/sys/devices/virtual/powercap accessible by default to containers

2023-10-3015:25:44
Google
osv.dev
20
powercap access
container security
rapl vulnerability
cve-2020-8694
cve-2020-8695
cve-2020-12912
linux kernel mitigation
user namespaces
sysfs read-only
default mount configuration
apparmor profile
container capabilities

2.1 Low

CVSS2

Attack Vector

LOCAL

Attack Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

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

5.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

NONE

Availability Impact

NONE

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

7.2 High

AI Score

Confidence

Low

0.0005 Low

EPSS

Percentile

17.6%

Intel’s RAPL (Running Average Power Limit) feature, introduced by the Sandy Bridge microarchitecture, provides software insights into hardware energy consumption. To facilitate this, Intel introduced the powercap framework in Linux kernel 3.13, which reads values via relevant MSRs (model specific registers) and provides unprivileged userspace access via sysfs. As RAPL is an interface to access a hardware feature, it is only available when running on bare metal with the module compiled into the kernel.

By 2019, it was realized that in some cases unprivileged access to RAPL readings could be exploited as a power-based side-channel against security features including AES-NI (potentially inside a SGX enclave) and KASLR (kernel address space layout randomization). Also known as the PLATYPUS attack, Intel assigned CVE-2020-8694 and CVE-2020-8695, and AMD assigned CVE-2020-12912.

Several mitigations were applied; Intel reduced the sampling resolution via a microcode update, and the Linux kernel prevents access by non-root users since 5.10. However, this kernel-based mitigation does not apply to many container-based scenarios:

  • Unless using user namespaces, root inside a container has the same level of privilege as root outside the container, but with a slightly more narrow view of the system
  • sysfs is mounted inside containers read-only; however only read access is needed to carry out this attack on an unpatched CPU

While this is not a direct vulnerability in container runtimes, defense in depth and safe defaults are valuable and preferred, especially as this poses a risk to multi-tenant container environments running directly on affected hardware. This is provided by masking /sys/devices/virtual/powercap in the default mount configuration, and adding an additional set of rules to deny it in the default AppArmor profile.

While sysfs is not the only way to read from the RAPL subsystem, other ways of accessing it require additional capabilities such as CAP_SYS_RAWIO which is not available to containers by default, or perf paranoia level less than 1, which is a non-default kernel tunable.

References

2.1 Low

CVSS2

Attack Vector

LOCAL

Attack Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

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

5.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

NONE

Availability Impact

NONE

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

7.2 High

AI Score

Confidence

Low

0.0005 Low

EPSS

Percentile

17.6%