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1 | # **Platform Runtime Mechanism**\r |
2 | \r | |
3 | Platform Runtime Mechanism (PRM) introduces the capability of moving platform-specific code out of SMM and into a\r | |
4 | code module that executes within the OS context. Moving this firmware to the OS context provides better transparency\r | |
5 | and mitigates the negative system impact currently accompanied with SMM solutions. Futhermore, the PRM code is\r | |
6 | packaged into modules with well-defined entry points, each representing a specific PRM functionality.\r | |
7 | \r | |
8 | The `PrmPkg` maintained in this branch provides a single cohesive set of generic PRM functionality that is intended\r | |
9 | to be leveraged by platform firmware with minimal overhead to integrate PRM functionality in the firmware.\r | |
10 | \r | |
11 | ## **IMPORTANT NOTE**\r | |
d10b8dc5 | 12 | > The code provided in this package and branch are for proof-of-concept purposes only. The code does not represent a\r |
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13 | formal design and is not validated at product quality. The development of this feature is shared in the edk2-staging\r |
14 | branch to simplify collaboration by allowing direct code contributions and early feedback throughout its development.\r | |
15 | \r | |
16 | ## How to Build PrmPkg\r | |
17 | As noted earlier, resources in `PrmPkg` are intended to be referenced by a platform firmware so it can adopt support\r | |
18 | for PRM. In that case, the platform firmware should add the `PrmConfigDxe` and `PrmLoaderDxe` drivers to its DSC and\r | |
19 | FDF files so they are built in the platform firmware build and dispatched during its runtime. All that is left is to\r | |
20 | add individual PRM modules to the DSC and FDF. These can be built from source or included as binaries into the platform\r | |
21 | firmware flash map.\r | |
22 | \r | |
23 | ### PrmPkg Standalone Build\r | |
24 | **All changes to `PrmPkg` must not regress the standalone package build**. Any time a change is made to `PrmPkg`, the\r | |
25 | package build must be tested. Since this is a forward looking package, to ease potential integration into the edk2\r | |
26 | project in the future, the build is tested against the tip of the master branch in the [edk2](https://github.com/tianocore/edk2)\r | |
27 | repository.\r | |
28 | \r | |
29 | To build `PrmPkg` as a standalone package:\r | |
30 | 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)\r | |
31 | \r | |
32 | 2. Clone the *master* branch on the edk2 repository locally \\r | |
33 | ``git clone https://github.com/tianocore/edk2.git``\r | |
34 | \r | |
35 | 3. Clone the *PlatformRuntimeMechanism* branch on the edk2-staging repository locally \\r | |
36 | ``git clone -b PlatformRuntimeMechanism --single-branch https://github.com/tianocore/edk2-staging.git``\r | |
37 | > __*Note*__: The *--single-branch* argument is recommended since edk2-staging hosts many branches for completely\r | |
38 | unrelated features. If you are just interested in PRM, this will avoid fetching all of the other branches.\r | |
39 | \r | |
40 | 4. Change to the edk2 workspace directory \\r | |
41 | ``cd edk2``\r | |
42 | \r | |
43 | 5. Run *edksetup* to set local environment variables needed for build\r | |
44 | * Windows:\r | |
45 | * ``edksetup.bat``\r | |
46 | * Linux:\r | |
47 | * If you have not already built BaseTools:\r | |
48 | * ``make -C BaseTools``\r | |
49 | * ``. edksetup.sh``\r | |
50 | \r | |
51 | 6. Set the PACKAGES_PATH environment variable to include the directory path that contains `PrmPkg`\r | |
52 | * Windows example:\r | |
53 | * ``set PACKAGES_PATH=c:\src\edk2-staging``\r | |
54 | \r | |
55 | 7. Change to the edk2-staging workspace directory\r | |
56 | * Example: ``cd ../edk2-staging``\r | |
57 | \r | |
58 | 8. Build PrmPkg \\r | |
59 | ``build -p PrmPkg/PrmPkg.dsc -a IA32 -a X64``\r | |
60 | > __*Note*__: Due to the way PRM modules are compiled with exports, **only building on Visual Studio compiler tool\r | |
61 | chains is currently supported**.\r | |
62 | \r | |
63 | ### Build Flags\r | |
64 | As PRM is a new feature at a proof-of-concept (POC) level of maturity, there's some changes to the normal build\r | |
65 | available as build flags. By default, if no flags are specified, the build is done with the currently expected plan of\r | |
66 | record (POR) configuration.\r | |
67 | \r | |
68 | The following list are the currently defined build flags (if any) that may be passed to the `build` command\r | |
69 | (e.g. -D FLAG=VALUE).\r | |
70 | \r | |
0797989c | 71 | * NONE - No build flags are currently used.\r |
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72 | \r |
73 | Additional detail: The context buffer structure is defined in [PrmContextBuffer.h](PrmPkg/Include/PrmContextBuffer.h).\r | |
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74 | This structure is passed as the context buffer to PRM handlers. The structure actually passed to PRM handlers is\r |
75 | allocated and populated by the OS where it gets all the information to populate the context buffer from other structures.\r | |
e8467976 | 76 | \r |
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77 | ### PRM Platform GUID\r |
78 | **IMPORTANT**\r | |
79 | \r | |
80 | A configuration item that requires user attention is the PRM platform GUID. Each platform that uses PRM must be\r | |
81 | uniquely identifiable so that various instances of a PRM module can target the correct platform in PRM module updates.\r | |
82 | \r | |
83 | To apply a unique platform GUID set the following PCD to a unique value in your platform DSC file.\r | |
84 | ``gPrmPkgTokenSpaceGuid.PcdPrmPlatformGuid``\r | |
85 | \r | |
86 | The default value assigned in [PrmPkg.dec](PrmPkg/PrmPkg.dec) is zero. By design, this is an invalid value that will\r | |
87 | cause an ASSERT if it is not updated.\r | |
88 | \r | |
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89 | ## Overview\r |
90 | At a high-level, PRM can be viewed from three levels of granularity:\r | |
91 | \r | |
92 | 1. PRM interface - Encompassing the entirety of firmware functionalities and data provided to OS runtime. Most\r | |
93 | information is provided through ACPI tables to be agnostic to a UEFI implementation.\r | |
94 | 2. PRM module - An independently updatable package of PRM handlers. The PRM interface will be composed of multiple\r | |
95 | PRM modules. This requirement allows for the separation of OEM and IHV PRM code, each of which can be serviced\r | |
96 | independently.\r | |
97 | 3. PRM handler - The implementation/callback of a single PRM functionality as identified by a GUID.\r | |
98 | \r | |
99 | ## Firmware Design\r | |
100 | The firmware has three key generic drivers to support PRM:\r | |
101 | \r | |
102 | 1. A PRM Loader driver - Functionality is split across three phases:\r | |
103 | 1. Discover - Find all PRM modules in the firmware image made available by the platform firmware author.\r | |
104 | * This phase includes verifying authenticity/integrity of the image, the image executable type, the export\r | |
105 | table is present and the PRM Export Module Descriptor is present and valid.\r | |
106 | 2. Process - Convert PRM handler GUID to name mappings in the PRM Module Export Descriptor to PRM handler Name\r | |
107 | to physical address mappings required to construct the PRM ACPI table.\r | |
108 | 3. Publish - Publish the PRM ACPI table using the information from the Process phase.\r | |
109 | \r | |
110 | 2. A PRM Configuration driver - A generic driver responsible for processing PRM module configuration information\r | |
111 | consumed through a `PRM_CONFIG_PROTOCOL` per PRM module instance. Therefore, the `PRM_CONFIG_PROTOCOL` serves\r | |
112 | as the dynamic interface for this driver to process PRM module resources and prepare the module's data to be\r | |
113 | configured properly for OS runtime.\r | |
114 | \r | |
115 | 3. A PRM Module - Not a single driver but a user written PE/COFF image that follows the PRM module authoring process.\r | |
116 | A PRM module groups together cohesive sets of PRM functionality into functions referred to as "PRM handlers".\r | |
117 | \r | |
118 | ## PrmPkg Code Organization\r | |
119 | The package follows a standard EDK II style package format. The list below contains some notable areas to\r | |
120 | explore in the package:\r | |
121 | \r | |
122 | * [ACPI Table Definitions](PrmPkg/PrmLoaderDxe/PrmAcpiTable.h)\r | |
123 | * [Common Interface Definitions](PrmPkg/Include)\r | |
124 | * [PRM Config Driver](PrmPkg/PrmConfigDxe)\r | |
125 | * [PRM Loader Driver](PrmPkg/PrmLoaderDxe)\r | |
126 | * [Sample PRM Modules](PrmPkg/Samples)\r | |
127 | \r | |
128 | While the package does provide sample PRM modules to be used as a reference, actual PRM modules should not be\r | |
129 | maintained in PrmPkg. It is intended to only contain PRM infrastructure code and a few samples of how to use\r | |
130 | that infrastructure. The PrmPkg is meant to be used as-is by firmware that supports PRM. Any shortcomings that\r | |
131 | prevent the package from being used as-is should be addressed directly in PrmPkg.\r | |
132 | \r | |
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133 | ## PRM Information UEFI Application\r |
134 | A UEFI application is provided in this package called "PrmInfo" that allows a user to display and test PRM\r | |
135 | modules on their system.\r | |
136 | \r | |
137 | [Link to application source code](PrmPkg/Application/PrmInfo).\r | |
138 | \r | |
139 | This application is intended to be helpful during PRM enabling by allowing the user to:\r | |
140 | 1. Confirm that their firmware port of the PRM infrastructure implemented in this package is functioning correctly.\r | |
141 | 2. Quickly get information about what PRM modules and handlers that are present on a given system.\r | |
142 | 3. Quickly test PRM handlers without booting into a full operating system.\r | |
143 | 4. Develop and exercise PRM handlers prior to the availability of an operating system that is PRM aware.\r | |
144 | \r | |
145 | Execute the application help command for detailed usage instructions and examples of how to use the application: \\r | |
146 | ``PrmInfo -?``\r | |
147 | \r | |
148 | *Example Usage:*\r | |
149 | \r | |
150 | ![](PrmPkg/Application/PrmInfo/PrmInfo_Usage_Example.gif)\r | |
151 | \r | |
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152 | ## PRM Module\r |
153 | \r | |
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154 | > __*Note*__: You can find simple examples of PRM modules in the Samples directory of this package.\r |
155 | > [Samples/Readme.md](PrmPkg/Samples/Readme.md) has more information.\r | |
156 | \r | |
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157 | By default, the EDK II implementation of UEFI does not allow images with the subsystem type\r |
158 | IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER to be built with exports. \r | |
159 | \r | |
160 | ```\r | |
161 | ERROR - Linker #1294 from LINK : fatal exports and import libraries are not supported with /SUBSYSTEM:EFI_RUNTIME_DRIVER\r | |
162 | ```\r | |
163 | This can adjusted in the MSVC linker options.\r | |
164 | \r | |
165 | __For the purposes of this POC__, the subsystem type is changed in the firmware build to allow the export table to be\r | |
166 | added but the subsystem type in the final image is still 0xC (EFI Runtime Driver). This is important to allow the DXE\r | |
167 | dispatcher to use its standard image verification and loading algorithms to load the image into permanent memory during\r | |
168 | the DXE execution phase.\r | |
169 | \r | |
170 | All firmware-loaded PRM modules are loaded into a memory buffer of type EfiRuntimeServicesCode. This means the\r | |
171 | operating system must preserve all PRM handler code and the buffer will be reflected in the UEFI memory map. The\r | |
172 | execution for invoking PRM handlers is the same as that required for UEFI Runtime Services, notably 4KiB or more of\r | |
173 | available stack space must be provided and the stack must be 16-byte aligned. \r | |
174 | \r | |
175 | __*Note:*__ Long term it is possible to similarly load the modules into a EfiRuntimeServicesCode buffer and perform\r | |
176 | relocation fixups with a new EFI module type for PRM if desired. It was simply not done since it is not essential\r | |
177 | for this POC.\r | |
178 | \r | |
179 | Where possible, PRM module information is stored and generated using industry compiler tool chains. This is a key\r | |
180 | motivation behind using PE/COFF export tables to expose PRM module information and using a single PRM module binary\r | |
181 | definition consistent between firmware and OS load.\r | |
182 | \r | |
183 | ### PRM Module Exports\r | |
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184 | A PRM module must contain at least two exports: A PRM Module Export Descriptor and at least one PRM handler. Here's\r |
185 | an example of an export table from a PRM module that has a single PRM handler:\r | |
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186 | \r |
187 | ```\r | |
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188 | 0000000000005000: 00 00 00 00 FF FF FF FF 00 00 00 00 3C 50 00 00 ............<P..\r |
189 | 0000000000005010: 01 00 00 00 02 00 00 00 02 00 00 00 28 50 00 00 ............(P..\r | |
190 | 0000000000005020: 30 50 00 00 38 50 00 00 78 13 00 00 20 40 00 00 0P..8P..x... @..\r | |
191 | 0000000000005030: 5D 50 00 00 7C 50 00 00 00 00 01 00 50 72 6D 53 ]P..|P......PrmS\r | |
192 | 0000000000005040: 61 6D 70 6C 65 43 6F 6E 74 65 78 74 42 75 66 66 ampleContextBuff\r | |
193 | 0000000000005050: 65 72 4D 6F 64 75 6C 65 2E 64 6C 6C 00 44 75 6D erModule.dll.Dum\r | |
194 | 0000000000005060: 70 53 74 61 74 69 63 44 61 74 61 42 75 66 66 65 pStaticDataBuffe\r | |
195 | 0000000000005070: 72 50 72 6D 48 61 6E 64 6C 65 72 00 50 72 6D 4D rPrmHandler.PrmM\r | |
196 | 0000000000005080: 6F 64 75 6C 65 45 78 70 6F 72 74 44 65 73 63 72 oduleExportDescr\r | |
197 | 0000000000005090: 69 70 74 6F 72 00 iptor.\r | |
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198 | \r |
199 | 00000000 characteristics\r | |
200 | FFFFFFFF time date stamp\r | |
a409f4b6 | 201 | 0.00 version\r |
d2cb6e67 | 202 | 1 ordinal base\r |
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203 | 2 number of functions\r |
204 | 2 number of names\r | |
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205 | \r |
206 | ordinal hint RVA name\r | |
a409f4b6 | 207 | \r |
d2cb6e67 | 208 | 1 0 00001378 DumpStaticDataBufferPrmHandler\r |
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209 | 2 1 00004020 PrmModuleExportDescriptor\r |
210 | \r | |
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211 | ```\r |
212 | ### PRM Image Format\r | |
213 | PRM modules are ultimately PE/COFF images. However, when packaged in firmware the PE/COFF image is placed into a\r | |
214 | Firmware File System (FFS) file. This is transparent to the operating system but done to better align with the typical\r | |
215 | packaging of PE32(+) images managed in the firmware binary image. In the dump of the PRM FV binary image shown earlier,\r | |
216 | the FFS sections placed by EDK II build tools ("DXE dependency", "User interface", "Version") that reside alongside the\r | |
217 | PE/COFF binary are shown. A PRM module can be placed into a firmware image as a pre-built PE/COFF binary or built\r | |
218 | during the firmware build process. In either case, the PE/COFF section is contained in a FFS file as shown in that\r | |
219 | image.\r | |
220 | \r | |
221 | ### PRM Module Implementation\r | |
222 | To simplify building the PRM Module Export Descriptor, a PRM module implementation can use the following macros to mark\r | |
223 | functions as PRM handlers. In this example, a PRM module registers three functions by name as PRM handlers with the\r | |
224 | associated GUIDs.\r | |
225 | \r | |
226 | ```\r | |
227 | //\r | |
228 | // Register the PRM export information for this PRM Module\r | |
229 | //\r | |
230 | PRM_MODULE_EXPORT (\r | |
231 | PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_1_GUID, PrmHandler1),\r | |
232 | PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_2_GUID, PrmHandler2),\r | |
233 | PRM_HANDLER_EXPORT_ENTRY (PRM_HANDLER_N_GUID, PrmHandlerN)\r | |
234 | );\r | |
235 | ```\r | |
236 | \r | |
237 | `PRM_MODULE_EXPORT` take a variable-length argument list of `PRM_HANDLER_EXPORT_ENTRY` entries that each describe an\r | |
238 | individual PRM handler being exported for the module. Ultimately, this information is used to define the structure\r | |
239 | necessary to statically allocate the PRM Module Export Descriptor Structure (and its PRM Handler Export Descriptor\r | |
240 | substructures) in the image.\r | |
241 | \r | |
242 | Another required export for PRM modules is automatically provided in `PrmModule.h`, a header file that pulls together\r | |
243 | all the includes needed to author a PRM module. This export is `PRM_MODULE_UPDATE_LOCK_EXPORT`. By including,\r | |
244 | `PrmModule.h`, a PRM module has the `PRM_MODULE_UPDATE_LOCK_DESCRIPTOR` automatically exported.\r | |
245 | \r | |
246 | ## PRM Handler Constraints\r | |
247 | At this time, PRM handlers are restricted to a maximum identifier length of 128 characters. This is checked when using\r | |
248 | the `PRM_HANDLER_EXPORT` macro by using a static assert that reports a violation at build-time.\r | |
249 | \r | |
250 | PRM handlers are **not** allowed to use UEFI Runtime Services and should not rely upon any UEFI constructs. For the\r | |
251 | purposes of this POC, this is currently not explicitly enforced but should be in the final changes.\r |