PrmPkg/Readme.md

   1 # **Platform Runtime Mechanism**
   2
   3 Platform Runtime Mechanism (PRM) introduces the capability of moving platform-specific code out of SMM and into a
   4 code module that executes within the OS context. Moving this firmware to the OS context provides better transparency
   5 and mitigates the negative system impact currently accompanied with SMM solutions. Futhermore, the PRM code is
   6 packaged into modules with well-defined entry points, each representing a specific PRM functionality.
   7
   8 For more details on PRM, refer to the [Platform Runtime Mechanism Specification on uefi.org](https://uefi.org/sites/default/files/resources/Platform%20Runtime%20Mechanism%20-%20with%20legal%20notice.pdf).
   9
  10 The `PrmPkg` maintained in this branch provides a single cohesive set of generic PRM functionality that is intended
  11 to be leveraged by platform firmware with minimal overhead to integrate PRM functionality in the firmware.
  12
  13 > By default, the build makes use of a new ACPI OperationRegion type specifically introduced for PRM called
  14 `PlatformRtMechanism`. Support for this OperationRegion is planned for the next release of the ACPI specification.
  15 However, support for `PlatformRtMechanism` is already included in the iASL Compiler/Disassembler for early prototyping
  16 (i.e. this package). If you would like the default build to work and/or to use PRM handlers that are invoked
  17 through ACPI, iASL compiler [20200528](https://acpica.org/node/181) or greater must be used. If you are only
  18 interested in compiling the code and/or using direct call style PRM handlers, you can simply remove
  19 `PrmSsdtInstallDxe` from `PrmPkg.dsc`.
  20
  21 The changes in the ACPI Specification include two elements:
  22
  23 1. `BIT20` in Platform-Wide _OSC Capabilities DWORD2 will be used by an OS to indicate support for PRM
  24 2. A new Operation Region Address Space Identifier Value is defined as `0xB` for `PlatformRtMechanism`
  25
  26 ## How to Build PrmPkg
  27
  28 As noted earlier, resources in `PrmPkg` are intended to be referenced by a platform firmware so it can adopt support
  29 for PRM. In that case, the platform firmware should add the `PrmConfigDxe` and `PrmLoaderDxe` drivers to its DSC and
  30 FDF files so they are built in the platform firmware build and dispatched during its runtime. All that is left is to
  31 add individual PRM modules to the DSC and FDF. These can be built from source or included as binaries into the platform
  32 firmware flash map.
  33
  34 ### PrmPkg Standalone Build
  35
  36 To build `PrmPkg` as a standalone package:
  37
  38 1. If new to EDK II, follow the directions in [Getting Started with EDK II](https://github.com/tianocore/tianocore.github.io/wiki/Getting-Started-with-EDK-II)
  39
  40 2. Clone the *master* branch on the edk2 repository locally \
  41    ``git clone https://github.com/tianocore/edk2.git``
  42
  43 3. Change to the edk2 workspace directory \
  44    ``cd edk2``
  45
  46 4. Run *edksetup* to set local environment variables needed for build
  47    * Windows:
  48      * ``edksetup.bat``
  49    * Linux:
  50      * If you have not already built BaseTools:
  51        * ``make -C BaseTools``
  52      * ``. edksetup.sh``
  53
  54 5. Build PrmPkg \
  55    ``build -p PrmPkg/PrmPkg.dsc -a IA32 -a X64``
  56    > ***Note***: Due to the way PRM modules are compiled with exports, **only building on Visual Studio compiler tool
  57    chains has been tested**.
  58
  59 > ***Note***: \
  60 > This package has been used without modification in several environments including client, server,
  61 > and virtual systems.
  62 >
  63 > You can add your own PRM modules into the build and check them with the `PrmInfo` UEFI application described
  64 > later in this document and dump the PRMT table in the OS to check if your PRM module is represented as expected.
  65
  66 ### PRM Platform GUID
  67
  68 **IMPORTANT** PRM has a concept of a "Platform GUID" which associates a specific platform with a set of PRM modules
  69 built for that platform. This GUID is used to ensure system compatibility for a given collection of PRM modules.
  70
  71 Therefore, each PRM module must only target a single platform and each platform must have a unique GUID. Even if a
  72 PRM module is unchanged between two different platforms now, there is no guarantee that will remain the case so always
  73 assign a unique Platform GUID for each platform.
  74
  75 The PRM Platform GUID is primarily used during PRM module runtime updates in the OS to ensure that the Platform GUID
  76 in the system's ACPI table (PRMT) matches the Platform GUID of the module requested for update. Even if runtime
  77 updates are not a planned feature for a given platform, still assign a unique Platform GUID for binary module
  78 identification (the Platform GUID is in the module's export descriptor) and to ensure such updates can be seamlessly
  79 supported in the future if needed.
  80
  81 In the `PrmPkg` implementation, the Platform GUID is automatically derived from the PLATFORM_GUID in the DSC file of
  82 the package being built.
  83
  84 ### Build Output
  85
  86 Like a typical EDK II package, the PrmPkg binary build output can be found in the Build directory in the edk2
  87 workspace. The organization in that directory follows the same layout as other EDK II packages.
  88
  89 For example, that path to PRM module sample binaries for a DEBUG VS2017 X64 build is: \
  90 ``edk2/Build/Prm/DEBUG_VS2017/X64/PrmPkg/Samples``
  91
  92 ## Overview
  93
  94 At a high-level, PRM can be viewed from three levels of granularity:
  95
  96 1. `PRM interface` - Encompassing the entirety of firmware functionalities and data provided to OS runtime. Most
  97    information is provided through ACPI tables to be agnostic to a UEFI implementation.
  98 2. `PRM module` - An independently updatable package of PRM handlers. The PRM interface will be composed of multiple
  99    PRM modules. This requirement allows for the separation of OEM and IHV PRM code, each of which can be serviced
 100    independently.
 101 3. `PRM handler` - The implementation/callback of a single PRM functionality as identified by a GUID.
 102
 103 ## Firmware Design
 104
 105 The firmware has three key generic drivers to support PRM:
 106
 107 1. A `PRM Loader driver` - Functionality is split across three phases:
 108    1. Discover - Find all PRM modules in the firmware image made available by the platform firmware author.
 109       * This phase includes verifying authenticity/integrity of the image, the image executable type, the export
 110         table is present and the PRM Export Module Descriptor is present and valid.
 111    2. Process - Convert PRM handler GUID to name mappings in the PRM Module Export Descriptor to PRM handler Name
 112       to physical address mappings required to construct the PRM ACPI table.
 113    3. Publish - Publish the PRM ACPI table using the information from the Process phase.
 114
 115 2. A `PRM Configuration driver` - A generic driver responsible for processing PRM module configuration information
 116    consumed through a `PRM_CONFIG_PROTOCOL` per PRM module instance. Therefore, the `PRM_CONFIG_PROTOCOL` serves
 117    as the dynamic interface for this driver to process PRM module resources and prepare the module's data to be
 118    configured properly for OS runtime.
 119
 120 3. A `PRM Module` - Not a single driver but a user written PE/COFF image that follows the PRM module authoring process.
 121    A PRM module groups together cohesive sets of PRM functionality into functions referred to as "PRM handlers".
 122
 123 ## PrmPkg Code Organization
 124
 125 The package follows a standard EDK II style package format. The list below contains some notable areas to
 126 explore in the package:
 127
 128 * [ACPI Table Definitions](PrmPkg/PrmLoaderDxe/PrmAcpiTable.h)
 129 * [Common Interface Definitions](PrmPkg/Include)
 130 * [PRM Config Driver](PrmPkg/PrmConfigDxe)
 131 * [PRM Loader Driver](PrmPkg/PrmLoaderDxe)
 132 * [Sample PRM Modules](PrmPkg/Samples)
 133
 134 While the package does provide sample PRM modules to be used as a reference, actual PRM modules should not be
 135 maintained in PrmPkg. It is intended to only contain PRM infrastructure code and a few samples of how to use
 136 that infrastructure. The PrmPkg is meant to be used as-is by firmware that supports PRM. Any shortcomings that
 137 prevent the package from being used as-is should be addressed directly in PrmPkg.
 138
 139 ## PRM Information UEFI Application
 140
 141 A UEFI application is provided in this package called `PrmInfo` that allows a user to display and test PRM
 142 modules on their system.
 143
 144 [Link to application source code](PrmPkg/Application/PrmInfo).
 145
 146 This application is intended to be helpful during PRM enabling by allowing the user to:
 147
 148   1. Confirm that their firmware port of the PRM infrastructure implemented in this package is functioning correctly.
 149   2. Quickly get information about what PRM modules and handlers that are present on a given system.
 150   3. Quickly test PRM handlers without booting into a full operating system.
 151   4. Develop and exercise PRM handlers prior to the availability of an operating system that is PRM aware.
 152
 153 Execute the application help command for detailed usage instructions and examples of how to use the application: \
 154   ``PrmInfo -?``
 155
 156 *Example Usage:*
 157
 158 ![PrmInfo Usage Example](https://raw.githubusercontent.com/tianocore/edk2-staging/PlatformRuntimeMechanism/PrmPkg/Application/PrmInfo/PrmInfo_Usage_Example.gif)
 159
 160 ## PRM Module
 161
 162 > ***Note***: You can find simple examples of PRM modules in the Samples directory of this package.
 163 > [Samples/Readme.md](PrmPkg/Samples/Readme.md) has more information.
 164
 165 By default, the EDK II implementation of UEFI does not allow images with the subsystem type
 166 `IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER` to be built with exports.
 167
 168 ```txt
 169 ERROR - Linker #1294 from LINK : fatal exports and import libraries are not supported with /SUBSYSTEM:EFI_RUNTIME_DRIVER
 170 ```
 171
 172 This can adjusted in the MSVC linker options.
 173
 174 The subsystem type is changed in the firmware build to allow the export table to be added but the subsystem type in the
 175 final image is still `0xC` (`EFI Runtime Driver`). This is important to allow the DXE dispatcher to use its standard
 176 image verification and loading algorithms to load the image into permanent memory during the DXE execution phase.
 177
 178 All firmware-loaded PRM modules are loaded into a memory buffer of type `EfiRuntimeServicesCode`. This means the
 179 operating system must preserve all PRM handler code and the buffer will be reflected in the UEFI memory map. The
 180 execution for invoking PRM handlers is the same as that required for UEFI Runtime Services, notably 4KiB or more of
 181 available stack space must be provided and the stack must be 16-byte aligned.
 182
 183 ***Note:*** Long term it is possible to similarly load the modules into a `EfiRuntimeServicesCode` buffer and perform
 184 relocation fixups with a new EFI module type for PRM if desired. It was simply not done since it is not essential
 185 for this POC.
 186
 187 Where possible, PRM module information is stored and generated using industry compiler tool chains. This is a key
 188 motivation behind using PE/COFF export tables to expose PRM module information and using a single PRM module binary
 189 definition consistent between firmware and OS load.
 190
 191 ### PRM Module Exports
 192
 193 A PRM module must contain at least two exports: A PRM Module Export Descriptor and at least one PRM handler. Here's
 194 an example of an export table from a PRM module that has a single PRM handler:
 195
 196 ```txt
 197   0000000000005000: 00 00 00 00 FF FF FF FF 00 00 00 00 3C 50 00 00  ............<P..
 198   0000000000005010: 01 00 00 00 02 00 00 00 02 00 00 00 28 50 00 00  ............(P..
 199   0000000000005020: 30 50 00 00 38 50 00 00 78 13 00 00 20 40 00 00  0P..8P..x... @..
 200   0000000000005030: 5D 50 00 00 7C 50 00 00 00 00 01 00 50 72 6D 53  ]P..|P......PrmS
 201   0000000000005040: 61 6D 70 6C 65 43 6F 6E 74 65 78 74 42 75 66 66  ampleContextBuff
 202   0000000000005050: 65 72 4D 6F 64 75 6C 65 2E 64 6C 6C 00 44 75 6D  erModule.dll.Dum
 203   0000000000005060: 70 53 74 61 74 69 63 44 61 74 61 42 75 66 66 65  pStaticDataBuffe
 204   0000000000005070: 72 50 72 6D 48 61 6E 64 6C 65 72 00 50 72 6D 4D  rPrmHandler.PrmM
 205   0000000000005080: 6F 64 75 6C 65 45 78 70 6F 72 74 44 65 73 63 72  oduleExportDescr
 206   0000000000005090: 69 70 74 6F 72 00                                iptor.
 207
 208     00000000 characteristics
 209     FFFFFFFF time date stamp
 210         0.00 version
 211            1 ordinal base
 212            2 number of functions
 213            2 number of names
 214
 215     ordinal hint RVA      name
 216
 217           1    0 00001378 DumpStaticDataBufferPrmHandler
 218           2    1 00004020 PrmModuleExportDescriptor
 219
 220 ```
 221
 222 ### PRM Image Format
 223
 224 PRM modules are ultimately PE/COFF images. However, when packaged in firmware the PE/COFF image is placed into a
 225 Firmware File System (FFS) file. This is transparent to the operating system but done to better align with the typical
 226 packaging of PE32(+) images managed in the firmware binary image. In the dump of the PRM FV binary image shown earlier,
 227 the FFS sections placed by EDK II build tools ("DXE dependency", "User interface", "Version") that reside alongside the
 228 PE/COFF binary are shown. A PRM module can be placed into a firmware image as a pre-built PE/COFF binary or built
 229 during the firmware build process. In either case, the PE/COFF section is contained in a FFS file as shown in that
 230 image.
 231
 232 ### PRM Module Implementation
 233
 234 To simplify building the PRM Module Export Descriptor, a PRM module implementation can use the following macros to mark
 235 functions as PRM handlers. In this example, a PRM module registers three functions by name as PRM handlers with the
 236 associated GUIDs.
 237
 238 ```c
 239 //
 240 // Register the PRM export information for this PRM Module
 241 //
 242 PRM_MODULE_EXPORT (
 243   PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_1_GUID, PrmHandler1),
 244   PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_2_GUID, PrmHandler2),
 245   PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_N_GUID, PrmHandlerN)
 246   );
 247 ```
 248
 249 `PRM_MODULE_EXPORT` take a variable-length argument list of `PRM_HANDLER_EXPORT_ENTRY` entries that each describe an
 250 individual PRM handler being exported for the module. Ultimately, this information is used to define the structure
 251 necessary to statically allocate the PRM Module Export Descriptor Structure (and its PRM Handler Export Descriptor
 252 substructures) in the image.
 253
 254 Another required export for PRM modules is automatically provided in `PrmModule.h`, a header file that pulls together
 255 all the includes needed to author a PRM module. This export is `PRM_MODULE_UPDATE_LOCK_EXPORT`. By including,
 256 `PrmModule.h`, a PRM module has the `PRM_MODULE_UPDATE_LOCK_DESCRIPTOR` automatically exported.
 257
 258 ## PRM Handler Constraints
 259
 260 At this time, PRM handlers are restricted to a maximum identifier length of 128 characters. This is checked when using
 261 the `PRM_HANDLER_EXPORT` macro by using a static assert that reports a violation at build-time.
 262
 263 PRM handlers are **not** allowed to use UEFI Runtime Services and should not rely upon any UEFI constructs. For the
 264 purposes of this POC, this is currently not explicitly enforced but should be in the final changes.