Security Vulnerability: Special Register Buffer Data Sampling aka CrossTalk (CVE-2020-0543)

This document (000019643) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 11

Situation

Security researchers have identified new side channel information leak attacks against special registers of Intel CPUs, which could be used to leak secrets between CPU Cores.

This affects instructions like:

- RDRAND / RDSEED (CPU based random generator)
- EGETKEY (SGX specific)

The content generated / used by these instructions could be determined by attackers on the same CPU core.
The content generated / used by these instructions could be determined
by attackers on the same CPU core.

This issue only affects a limited set of Intel CPUs, largely Client CPU's. :

Common Name:	Family_Model:	Stepping:
Haswell	06_3CH	All
Haswell_L	06_45H	All
Haswell_G	06_46H	All
Broadwell_G	06_47H	All
Broadwell	06_3DH	All
Skylake_L	06_4EH	All
Skylake	06_4EH	All
Kabylake_L	06_8EH	<=0xC
Kabylake	06_9EH	<=0xD1

Resolution

The mitigation uses updated CPU Microcode to serialize the RDRAND, RDSEED and EGETKEY instructions to avoid side channel information leaks.

The Linux kernel updates provided by SUSE additionally also remove RDRAND calls from various code paths in the kernel and replace them by faster calls into the kernel random generator.

SUSE is releasing :
- Linux Kernel packages that allow reporting and control of the mitigation.
- Intel CPU Microcode updates via ucode-intel and microcode_ctl (SLE11) packages.
- XEN Updates that allow reporting and control of the mitigation.

Cause

CVE-2020-0543

Status

Security Alert

Additional Information

For detecting the mitigation status, the Linux kernel updates provide a file in sysfs:

/sys/devices/system/cpu/vulnerabilities/srbds

that can contain the following states:
Not affected
       - The system is not affected by this issue.

   Vulnerable
       - The system is vulnerable

   Vulnerable: No microcode
       - There is no microcode mitigation loaded for the vulnerability.

   Mitigation: Microcode
       - The Microcode mitigation the issue is is active.

   Mitigation: TSX disabled
       - Also disabling TSX mitigates the vulnerability, if the processor supports it.

   Unknown: Dependent on hypervisor status
- The hypervisor is not reporting the respective CPU flags for the kernel to determine affectedness.

On XEN the "srbds-ctrl" flag will be reported.

The mitigation is default enabled with updated microcode.

As it has a performance impact on code that use these instructions, there are kernel command line boot parameters options available to disable these mitigations:

Linux kernel command line boot option:
srbds=off
       Disables the mitigation

Please note: The kernel command line option "mitigations=off" also implies "srbds=off".

XEN Hypervisor, there is a bootline sub-option for "spec-ctrl":

   srb-lock=false
       Disables the mitigation.

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.