On Mon, 17 May 2021 at 18:14, Sudeep Holla <sudeep.holla@xxxxxxx> 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@xxxxxxx > Cc: Rob Herring <robh+dt@xxxxxxxxxx> > Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx> Hi Sudeep/Viresh/Rob, I noticed this binding recently got accepted, so I guess I have missed the opportunity to provide you with a few comments. In any case, I would like to ask a few questions. In particular, am I trying to understand why the power-domains bindings [1] can't be used for this? The power-domains are capable of dealing with "performance" through the "operating-points-v2" DT property, which maps to the generic OPP bindings [2]. I wonder why that isn't sufficient here? Can you please elaborate? [1] Documentation/devicetree/bindings/power/power-domain.yaml [2] Documentation/devicetree/bindings/opp/opp-v2-base.yaml Kind regards Uffe > --- > 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 > $ref for performance-domain > - Changed the example to use real existing compatibles instead > of made-up ones > > Regards, > Sudeep > > [1] https://lore.kernel.org/r/20201105173539.1426301-1-sudeep.holla@xxxxxxx > [2] https://lore.kernel.org/r/20201116181356.804590-1-sudeep.holla@xxxxxxx > [3] https://lore.kernel.org/r/20210407135913.2067694-1-sudeep.holla@xxxxxxx > > .../devicetree/bindings/arm/cpus.yaml | 7 ++ > .../bindings/dvfs/performance-domain.yaml | 74 +++++++++++++++++++ > 2 files changed, 81 insertions(+) > create mode 100644 Documentation/devicetree/bindings/dvfs/performance-domain.yaml > > diff --git a/Documentation/devicetree/bindings/arm/cpus.yaml b/Documentation/devicetree/bindings/arm/cpus.yaml > index f3c7249c73d6..9a2432a88074 100644 > --- a/Documentation/devicetree/bindings/arm/cpus.yaml > +++ b/Documentation/devicetree/bindings/arm/cpus.yaml > @@ -257,6 +257,13 @@ description: |+ > > where voltage is in V, frequency is in MHz. > > + performance-domains: > + maxItems: 1 > + description: > + List of phandles and performance domain specifiers, as defined by > + bindings of the performance domain provider. See also > + dvfs/performance-domain.yaml. > + > power-domains: > description: > List of phandles and PM domain specifiers, as defined by bindings of the > diff --git a/Documentation/devicetree/bindings/dvfs/performance-domain.yaml b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml > new file mode 100644 > index 000000000000..c8b91207f34d > --- /dev/null > +++ b/Documentation/devicetree/bindings/dvfs/performance-domain.yaml > @@ -0,0 +1,74 @@ > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/dvfs/performance-domain.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Generic performance domains > + > +maintainers: > + - Sudeep Holla <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 > + > +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 ] > + > + performance-domains: > + $ref: '/schemas/types.yaml#/definitions/phandle-array' > + maxItems: 1 > + description: > + A phandle and performance domain specifier as defined by bindings of the > + performance controller/provider specified by phandle. > + > +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>; > + }; > + }; > -- > 2.25.1 >
