52 lines
2.7 KiB
Markdown
52 lines
2.7 KiB
Markdown
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# Access-controlled NVRAM implementation
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This repository contains various pieces related to the Access-controlled NVRAM
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HAL. In a nutshell, the Access-controlled NVRAM HAL allows creation of NVRAM
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spaces that can hold arbitrary data blobs of limited size. Access restrictions
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can be configured on each NVRAM space to prevent the contents from being
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accessed or modified, up to the point of requiring full hardware reset to clear
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a locked NVRAM space. This can be used for various security features that
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require a trusted storage location for critical data that an attacker can't
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tamper with. For details of the NVRAM HAL API, see
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[hardware/libhardware/include/hardware/nvram.h](https://android.googlesource.com/platform/hardware/libhardware/+/master/include/hardware/nvram.h).
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## [client](/client)
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Contains a simple command-line application to interact with the NVRAM HAL
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implementation. This is useful for experimentation and use in scripts.
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`nvram-client` receives commands and parameters on the command line and
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translates them to NVRAM HAL calls. Results are printed on stdout.
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## [core](/core)
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A reference implementation of the NVRAM functionality. This reference
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implementation can be used to create NVRAM HAL implementations that run in a
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trusted execution environment. It is also the basis for the testing NVRAM HAL
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module, which implements the entire NVRAM HAL API surface in userspace for the
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sake of illustration (but obviously doesn't meet the persistence and
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tamper-evidence requirements).
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Note that the reference implementation leaves persistent storage to be handled
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by the embedding code, which needs to provide an implementation of the storage
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interface defined in
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[system/nvram/core/include/nvram/core/storage.h](core/include/nvram/core/storage.h).
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## [hal](/hal)
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The [hal](/hal) directory contains glue code that simplifies creation of NVRAM
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HAL modules. The code implements the API surface specified by the nvram.h HAL
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header and translates calls into the request/response message format defined in
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the [messages](/messages) directory. Thus, to create a working NVRAM HAL module,
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it is sufficient to provide an implementation that understands `nvram::Request`
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and `nvram::Response` objects, the glue code will adapt it to the full NVRAM API
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surface.
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## [messages](/messages)
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Defines an IPC message format that can be used to serialize NVRAM HAL calls and
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their parameters in preparation for sending them elsewhere (e.g., a TEE) for
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execution. There is a request and a response struct corresponding to each NVRAM
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HAL function. The `nvram::Request` and `nvram::Response` wrappers keep track of
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the actual request or response type, respectively, as well as the request or
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response parameters specific to the type.
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