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. Rob > + 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. > + > + device1: foo@56780000 { > + compatible = "foo,bar-controller"; > + reg = <0x56780000 0x1000>; > + performance-domains = <&performance 1>; > + }; > + > -- > 2.25.1 >
