On Wed, Nov 18, 2020 at 03:20:09PM -0600, Rob Herring wrote:
> On Mon, Nov 16, 2020 at 06:13:56PM +0000, 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
> >
> > Cc: Rob Herring <[email protected]>
> > Signed-off-by: Sudeep Holla <[email protected]>
> > ---
> > .../bindings/dvfs/performance-domain.yaml | 76 +++++++++++++++++++
> > 1 file changed, 76 insertions(+)
> > create mode 100644
> > Documentation/devicetree/bindings/dvfs/performance-domain.yaml
> >
> > v1[1]->v2:
> > - Changed to Dual License
> > - Added select: true, enum for #performance-domain-cells and
> > $ref for performance-domain
> > - Changed the example to use real existing compatibles instead
> > of made-up ones
> >
> > [1]
> > https://lore.kernel.org/lkml/[email protected]
> >
> > diff --git a/Documentation/devicetree/bindings/dvfs/performance-domain.yaml
> > b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml
> > new file mode 100644
> > index 000000000000..29fb589a5192
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml
> > @@ -0,0 +1,76 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/dvfs/performance-domain.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Generic performance domains
> > +
> > +maintainers:
> > + - Sudeep Holla <[email protected]>
> > +
> > +description: |+
> > + This binding is intended for performance management of groups of devices
> > or
> > + CPUs that run in the same performance domain. Performance domains must
> > not
> > + be confused with power domains. A performance domain is defined by a set
> > + of devices that always have to run at the same performance level. For a
> > given
> > + performance domain, there is a single point of control that affects all
> > the
> > + devices in the domain, making it impossible to set the performance level
> > of
> > + an individual device in the domain independently from other devices in
> > + that domain. For example, a set of CPUs that share a voltage domain, and
> > + have a common frequency control, is said to be in the same performance
> > + domain.
> > +
> > + This device tree binding can be used to bind performance domain consumer
> > + devices with their performance domains provided by performance domain
> > + providers. A performance domain provider can be represented by any node
> > in
> > + the device tree and can provide one or more performance domains. A
> > consumer
> > + node can refer to the provider by a phandle and a set of phandle
> > arguments
> > + (so called performance domain specifiers) of length specified by the
> > + \#performance-domain-cells property in the performance domain provider
> > node.
> > +
> > +select: true
>
> So apply to every node and...
>
New to yaml, still figuring out 😄.
>From the bot build error, I now realise that I can't take shortcut to build:
$ make dt_binding_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/arm/dvfs/performance-domain.yaml
[...]
> > +
> > +additionalProperties: true
> > +
> > +examples:
> > + - |
> > + performance: performance-controller@12340000 {
> > + compatible = "qcom,cpufreq-hw";
> > + reg = <0x12340000 0x1000>;
> > + #performance-domain-cells = <1>;
> > + };
> > +
> > + // The node above defines a performance controller that is a
> > performance
> > + // domain provider and expects one cell as its phandle argument.
> > + cpus {
> > + #address-cells = <2>;
> > + #size-cells = <0>;
> > +
> > + cpu@0 {
> > + device_type = "cpu";
> > + compatible = "arm,cortex-a57";
> > + reg = <0x0 0x0>;
> > + performance-domains = <&performance 1>;
>
> Looks like the cpu schema needs an addition.
>
OK.
--
Regards,
Sudeep
