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 /**
  28   Serialize and persistently save platform configuration.
  29
  30   @param[in] PlatformConfig  The platform configuration to serialize and save.
  31
  32   @return  Status codes returned by gRT->SetVariable().
  33 **/
  34 EFI_STATUS
  35 EFIAPI
  36 PlatformConfigSave (
  37   IN PLATFORM_CONFIG *PlatformConfig
  38   )
  39 {
  40   EFI_STATUS Status;
  41
  42   //
  43   // We could implement any kind of translation here, as part of serialization.
  44   // For example, we could expose the platform configuration in separate
  45   // variables with human-readable contents, allowing other tools to access
  46   // them more easily. For now, just save a binary dump.
  47   //
  48   Status = gRT->SetVariable (mVariableName, &gOvmfPlatformConfigGuid,
  49                   EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
  50                     EFI_VARIABLE_RUNTIME_ACCESS,
  51                   sizeof *PlatformConfig, PlatformConfig);
  52   return Status;
  53 }
  54
  55
  56 /**
  57   Load and deserialize platform configuration.
  58
  59   When the function fails, output parameters are indeterminate.
  60
  61   @param[out] PlatformConfig    The platform configuration to receive the
  62                                 loaded data.
  63
  64   @param[out] OptionalElements  This bitmap describes the presence of optional
  65                                 configuration elements that have been loaded.
  66                                 PLATFORM_CONFIG_F_DOWNGRADE means that some
  67                                 unknown elements, present in the wire format,
  68                                 have been ignored.
  69
  70   @retval  EFI_SUCCESS         Loading & deserialization successful.
  71   @return                      Error codes returned by GetVariable2().
  72 **/
  73 EFI_STATUS
  74 EFIAPI
  75 PlatformConfigLoad (
  76   OUT PLATFORM_CONFIG *PlatformConfig,
  77   OUT UINT64          *OptionalElements
  78   )
  79 {
  80   VOID       *Data;
  81   UINTN      DataSize;
  82   EFI_STATUS Status;
  83
  84   //
  85   // Any translation done in PlatformConfigSave() would have to be mirrored
  86   // here. For now, just load the binary dump.
  87   //
  88   // Versioning of the binary wire format is implemented based on size
  89   // (only incremental changes, ie. new fields), and on GUID.
  90   // (Incompatible changes require a GUID change.)
  91   //
  92   Status = GetVariable2 (mVariableName, &gOvmfPlatformConfigGuid, &Data,
  93              &DataSize);
  94   if (EFI_ERROR (Status)) {
  95     return Status;
  96   }
  97
  98   *OptionalElements = 0;
  99   if (DataSize > sizeof *PlatformConfig) {
 100     //
 101     // Handle firmware downgrade -- keep only leading part.
 102     //
 103     CopyMem (PlatformConfig, Data, sizeof *PlatformConfig);
 104     *OptionalElements |= PLATFORM_CONFIG_F_DOWNGRADE;
 105   } else {
 106     CopyMem (PlatformConfig, Data, DataSize);
 107
 108     //
 109     // Handle firmware upgrade -- zero out missing fields.
 110     //
 111     ZeroMem ((UINT8 *)PlatformConfig + DataSize,
 112       sizeof *PlatformConfig - DataSize);
 113   }
 114
 115   //
 116   // Based on DataSize, report the optional features that we recognize.
 117   //
 118   if (DataSize >= (OFFSET_OF (PLATFORM_CONFIG, VerticalResolution) +
 119                    sizeof PlatformConfig->VerticalResolution)) {
 120     *OptionalElements |= PLATFORM_CONFIG_F_GRAPHICS_RESOLUTION;
 121   }
 122
 123   FreePool (Data);
 124   return EFI_SUCCESS;
 125 }