armstub8: Add PSCI monitor support for BCM2711

[hanzyd]

This monitor is used to workaround few issues in
Cortex-A72 CPU used in BCM2711:

• CVE-2017-5715 aka Spectre-v2. Invalidate the Branch Target
  Buffer (BTB) on entry to EL3 by disabling and enabling the MMU.
• CVE-2018-3639 aka Spectre-v4. Set or clean bit 55
  (Disable load pass store) of CPUACTLR_EL1, when requested
  by SMCCC_ARCH_WORKAROUND_2.
• Prevent speculative execution past ERET.
• Implement workaround for AT speculative behaviour

This work is based on Oleksandr RPi3 psci-monitor [1] and
Arm Trusted Firmware [2].

Mitigation's are implemented according "ARM DEN 0070A" [3].

CVE workarounds could be controlled via Linux command line
options [4]: nospectre_v2 and ssbd=

Validation was done using Ghostbusters [5] and Google's Safeside
project [6].

Supported functions include:
PSCI_VERSION
PSCI_CPU_OFF
PSCI_CPU_ON
PSCI_AFFINITY_INFO
PSCI_MIGRATE_INFO_TYPE
PSCI_MIGRATE_INFO_UP_CPU
PSCI_SYSTEM_OFF
PSCI_SYSTEM_RESET
PSCI_FEATURES
SMCCC_VERSION
SMCCC_ARCH_WORKAROUND_1
SMCCC_ARCH_WORKAROUND_2

As side effect of this now Linux kexec is working.

Performance degradation was evaluated using Phoronix hackbench
and it is around 6% in combined case, I would say.

"Hackbench - Count: 4 - Type: Process"

00 = spectre_v2: Vulnerable, spec_store_bypass: Vulnerable
01 = spectre_v2: Mitigated, spec_store_bypass: Vulnerable
02 = spectre_v2: Vulnerable, spec_store_bypass: Mitigated
03 = spectre_v2: Mitigated, spec_store_bypass: Mitigated
04 = no PSCI monitor at all
05 = no PSCI monitor at all

 Run-1   | Run-2   | Run-3, seconds

---

00 | 100.689 | 100.215 | 100.749
01 | 103.386 | 104.627 | 104.387
02 | 104.519 | 105.383 | 104.611
03 | 107.084 | 106.081 | 107.269
04 | 101.301 | 101.894 | 102.564
05 | 100.302 | 101.85 | 99.912

Details could be found here [7].

[1] https://github.com/gonzoua/rpi3-psci-monitor
[2] https://github.com/Arm-Software/arm-trusted-firmware
[3] "Firmware interfaces for mitigating cache speculation vulnerabilities"
[4] https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
[5] https://github.com/Sultanic/Ghostbusters.git
[6] https://github.com/google/safeside.git
[7] https://openbenchmarking.org/result/2103024-HA-PSCIMON0014,2103020-HA-PSCIMON0130,2103027-HA-PSCIMON0242,2103028-HA-PSCIMON0310,2103021-HA-PSCIMON0401,2103021-HA-PSCIMON0524

Signed-off-by: Ivan T. Ivanov [email protected]

[pelwell]

Why do you think this should be the standard ARMv8 stub, given that it is so easy for distributions to provide there own?

And are you the author? Your GitHub userid does not make this obvious.

[hanzyd]

Well, they are distributions that are using this stub, like openSUSE.
In some sense is easer to add simple mitigations here, than use
big/fat TF-A. I think there will be others that could benefit for this.

This work is heavily based on TF-A and RPi3 monitor, as stated in commit
message, but, yes, I am the author of this.