Configuring Spectre Protection Level

The Spectre protections on POWER9 can be partly or fully disengaged if desired. Note that disengaging the protections will leave you vulnerable to attack via Spectre variant 2, and could result in data leakage and/or system compromise. The override is controlled by the BMC and requires a reboot of the POWER9 to take effect.

To override the protection level:

1. Create/edit the file /var/lib/obmc/cfam_overrides on the BMC.
2. Add the following contents:

# Control speculative execution mode
0 0x283a 0x00000001  # bits 28:31 are used for init level -- in this case 1 (Kernel protection only)
0 0x283F 0x20000000  # Indicate override register is valid

3. Re-IPL (fully power off and restart the host system) to apply changes.

Key:

• Init level 0 — Kernel and User protection (safest, default)
• Init level 1 — Kernel protection only
• Init level 2 — No protection

Note: Overriding the protection level in this manner may cause the POWER9 CPU to be detected by the operating system as an earlier revision than it should be - for instance, if your CPU is DD2.3, /proc/cpuinfo may report it as DD2.2. This can cause unexpected behavior or errors when running virtual machines. There is no performance benefit to disabling protections and in general, they should be left in place.

See also

• Speculative Execution Vulnerabilities of 2018