On Mon, Nov 09, 2020 at 02:15:18PM -0600, Rob Herring wrote: > On Thu, Nov 05, 2020 at 05:35:39PM +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 <robh+dt@xxxxxxxxxx> > > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx> > > --- > > .../bindings/dvfs/performance-domain.yaml | 67 +++++++++++++++++++ > > 1 file changed, 67 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/dvfs/performance-domain.yaml > > > > diff --git a/Documentation/devicetree/bindings/dvfs/performance-domain.yaml b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml > > new file mode 100644 > > index 000000000000..fa0151f63ac9 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml > > @@ -0,0 +1,67 @@ > > +# SPDX-License-Identifier: GPL-2.0 > > Dual license new bindings. > > > +%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 <sudeep.holla@xxxxxxx> > > + > > +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 > > Otherwise, this schema is never used. > > > + > > +properties: > > + "#performance-domain-cells": > > + description: > > + Number of cells in a performance domain specifier. Typically 0 for nodes > > + representing a single performance domain and 1 for nodes providing > > + multiple performance domains (e.g. performance controllers), but can be > > + any value as specified by device tree binding documentation of particular > > + provider. > > enum: [ 0, 1 ] > > If we need more, it can be extended. > > > + > > + performance-domains: > > Needs a type ref (phandle-array). > > > + description: > > + A phandle and performance domain specifier as defined by bindings of the > > + performance controller/provider specified by phandle. > > + > > +required: > > + - "#performance-domain-cells" > > + > > +additionalProperties: true > > + > > +examples: > > + - | > > + performance: performance-controller@12340000 { > > + compatible = "foo,performance-controller"; > > At some point in the future, this is going to generate warnings as an > undocumented binding. So we'll have to remove it, add a schema for it, > or replace with a real example. This is a standard DT design pattern, so > I'd lean toward removing the example. > Thanks for the review, I have fixed all other things pointed out. I have retained the example in v2 with real compatibles as I believe it is good to have an example for the new binding. I am happy to drop it if it still looks wrong. -- Regards, Sudeep
