Re: [PATCH v4] dt-bindings: dvfs: Add support for generic performance domains

On Mon, 17 May 2021 16:54:58 +0100, Sudeep Holla wrote:

The CLKSCREW attack [0] exposed security vulnerabilities in energy management
implementations where untrusted software had direct access to clock and
voltage hardware controls. In this attack, the malicious software was able to
place the platform into unsafe overclocked or undervolted configurations. Such
configurations then enabled the injection of predictable faults to reveal
secrets.

Many Arm-based systems used to or still use voltage regulator and clock
frameworks in the kernel. These frameworks allow callers to independently
manipulate frequency and voltage settings. Such implementations can render
systems susceptible to this form of attack.

Attacks such as CLKSCREW are now being mitigated by not having direct and
independent control of clock and voltage in the kernel and moving that
control to a trusted entity, such as the SCP firmware or secure world
firmware/software which are to perform sanity checking on the requested
performance levels, thereby preventing any attempted malicious programming.

With the advent of such an abstraction, there is a need to replace the
generic clock and regulator bindings used by such devices with a generic
performance domains bindings.

[0] https://www.usenix.org/conference/usenixsecurity17/technical-sessions/presentation/tang

Link: https://lore.kernel.org/r/20201116181356.804590-1-sudeep.holla@arm.com (local)
Cc: Rob Herring <robh+dt@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Sudeep Holla <redacted>
---
Hi All,

Sorry for yet another delay, I don't want to mist this for v5.14 as Mediatek
cpufreq driver was depending on this IIRC.

v3[3]->v4:
	- Dropped unnecessary phandle-array reference
	- Added maxItems = 1 for the property

v2[2]->v3[3]:
	- Dropped required properties
	- Added non cpu device example
	- Updated cpu bindings too

v1[1]->v2[2]:
	- Changed to Dual License
	- Added select: true, enum for #performance-domain-cells and
	  $ref for performance-domain
	- Changed the example to use real existing compatibles instead
	  of made-up ones

Regards,
Sudeep

[1] https://lore.kernel.org/r/20201105173539.1426301-1-sudeep.holla@arm.com (local)
[2] https://lore.kernel.org/r/20201116181356.804590-1-sudeep.holla@arm.com (local)
[3] https://lore.kernel.org/r/20210407135913.2067694-1-sudeep.holla@arm.com (local)

 .../devicetree/bindings/arm/cpus.yaml         |  7 ++
 .../bindings/dvfs/performance-domain.yaml     | 74 +++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/dvfs/performance-domain.yaml

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Documentation/devicetree/bindings/dvfs/performance-domain.example.dt.yaml:0:0: /example-0/performance-controller@12340000: failed to match any schema with compatible: ['qcom,cpufreq-hw']

See https://patchwork.ozlabs.org/patch/1479615

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.