OvmfPkg/PlatformDxe/PlatformConfig.c

   1 /** @file
   2
   3   Utility functions for serializing (persistently storing) and deserializing
   4   OVMF's platform configuration.
   5
   6   Copyright (C) 2014, Red Hat, Inc.
   7
   8   SPDX-License-Identifier: BSD-2-Clause-Patent
   9
  10 **/
  11
  12 #include <Library/BaseMemoryLib.h>
  13 #include <Library/DebugLib.h>
  14 #include <Library/MemoryAllocationLib.h>
  15 #include <Library/UefiLib.h>
  16 #include <Library/UefiRuntimeServicesTableLib.h>
  17 #include <Guid/OvmfPlatformConfig.h>
  18
  19 #include "PlatformConfig.h"
  20
  21 //
  22 // Name of the UEFI variable that we use for persistent storage.
  23 //
  24 STATIC CHAR16  mVariableName[] = L"PlatformConfig";
  25
  26 /**
  27   Serialize and persistently save platform configuration.
  28
  29   @param[in] PlatformConfig  The platform configuration to serialize and save.
  30
  31   @return  Status codes returned by gRT->SetVariable().
  32 **/
  33 EFI_STATUS
  34 EFIAPI
  35 PlatformConfigSave (
  36   IN PLATFORM_CONFIG  *PlatformConfig
  37   )
  38 {
  39   EFI_STATUS  Status;
  40
  41   //
  42   // We could implement any kind of translation here, as part of serialization.
  43   // For example, we could expose the platform configuration in separate
  44   // variables with human-readable contents, allowing other tools to access
  45   // them more easily. For now, just save a binary dump.
  46   //
  47   Status = gRT->SetVariable (
  48                   mVariableName,
  49                   &gOvmfPlatformConfigGuid,
  50                   EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
  51                   EFI_VARIABLE_RUNTIME_ACCESS,
  52                   sizeof *PlatformConfig,
  53                   PlatformConfig
  54                   );
  55   return Status;
  56 }
  57
  58 /**
  59   Load and deserialize platform configuration.
  60
  61   When the function fails, output parameters are indeterminate.
  62
  63   @param[out] PlatformConfig    The platform configuration to receive the
  64                                 loaded data.
  65
  66   @param[out] OptionalElements  This bitmap describes the presence of optional
  67                                 configuration elements that have been loaded.
  68                                 PLATFORM_CONFIG_F_DOWNGRADE means that some
  69                                 unknown elements, present in the wire format,
  70                                 have been ignored.
  71
  72   @retval  EFI_SUCCESS         Loading & deserialization successful.
  73   @return                      Error codes returned by GetVariable2().
  74 **/
  75 EFI_STATUS
  76 EFIAPI
  77 PlatformConfigLoad (
  78   OUT PLATFORM_CONFIG  *PlatformConfig,
  79   OUT UINT64           *OptionalElements
  80   )
  81 {
  82   VOID        *Data;
  83   UINTN       DataSize;
  84   EFI_STATUS  Status;
  85
  86   //
  87   // Any translation done in PlatformConfigSave() would have to be mirrored
  88   // here. For now, just load the binary dump.
  89   //
  90   // Versioning of the binary wire format is implemented based on size
  91   // (only incremental changes, ie. new fields), and on GUID.
  92   // (Incompatible changes require a GUID change.)
  93   //
  94   Status = GetVariable2 (
  95              mVariableName,
  96              &gOvmfPlatformConfigGuid,
  97              &Data,
  98              &DataSize
  99              );
 100   if (EFI_ERROR (Status)) {
 101     return Status;
 102   }
 103
 104   *OptionalElements = 0;
 105   if (DataSize > sizeof *PlatformConfig) {
 106     //
 107     // Handle firmware downgrade -- keep only leading part.
 108     //
 109     CopyMem (PlatformConfig, Data, sizeof *PlatformConfig);
 110     *OptionalElements |= PLATFORM_CONFIG_F_DOWNGRADE;
 111   } else {
 112     CopyMem (PlatformConfig, Data, DataSize);
 113
 114     //
 115     // Handle firmware upgrade -- zero out missing fields.
 116     //
 117     ZeroMem (
 118       (UINT8 *)PlatformConfig + DataSize,
 119       sizeof *PlatformConfig - DataSize
 120       );
 121   }
 122
 123   //
 124   // Based on DataSize, report the optional features that we recognize.
 125   //
 126   if (DataSize >= (OFFSET_OF (PLATFORM_CONFIG, VerticalResolution) +
 127                    sizeof PlatformConfig->VerticalResolution))
 128   {
 129     *OptionalElements |= PLATFORM_CONFIG_F_GRAPHICS_RESOLUTION;
 130   }
 131
 132   FreePool (Data);
 133   return EFI_SUCCESS;
 134 }