/** @file
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Large Variable Read Lib
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This library is used to retrieve large data sets using the UEFI Variable
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Services. At time of writing, most UEFI Variable Services implementations do
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not allow more than 64KB of data to be stored in a single UEFI variable. This
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library will split data sets across multiple variables as needed.
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In the case where more than one variable is needed to store the data, an
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integer number will be added to the end of the variable name. This number
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will be incremented for each variable as needed to retrieve the entire data
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set.
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Copyright (c) 2021, Intel Corporation. All rights reserved.<BR>
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SPDX-License-Identifier: BSD-2-Clause-Patent
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**/
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#include <Library/BaseLib.h>
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#include <Library/BaseMemoryLib.h>
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#include <Library/DebugLib.h>
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#include <Library/PrintLib.h>
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#include <Library/VariableReadLib.h>
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#include "LargeVariableCommon.h"
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/**
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Returns the value of a large variable.
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@param[in] VariableName A Null-terminated string that is the name of the vendor's
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variable.
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@param[in] VendorGuid A unique identifier for the vendor.
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@param[in, out] DataSize On input, the size in bytes of the return Data buffer.
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On output the size of data returned in Data.
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@param[out] Data The buffer to return the contents of the variable. May be NULL
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with a zero DataSize in order to determine the size buffer needed.
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@retval EFI_SUCCESS The function completed successfully.
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@retval EFI_NOT_FOUND The variable was not found.
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@retval EFI_BUFFER_TOO_SMALL The DataSize is too small for the result.
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@retval EFI_INVALID_PARAMETER VariableName is NULL.
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@retval EFI_INVALID_PARAMETER VendorGuid is NULL.
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@retval EFI_INVALID_PARAMETER DataSize is NULL.
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@retval EFI_INVALID_PARAMETER The DataSize is not too small and Data is NULL.
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@retval EFI_DEVICE_ERROR The variable could not be retrieved due to a hardware error.
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@retval EFI_SECURITY_VIOLATION The variable could not be retrieved due to an authentication failure.
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**/
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EFI_STATUS
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EFIAPI
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GetLargeVariable (
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IN CHAR16 *VariableName,
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IN EFI_GUID *VendorGuid,
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IN OUT UINTN *DataSize,
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OUT VOID *Data OPTIONAL
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)
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{
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CHAR16 TempVariableName[MAX_VARIABLE_NAME_SIZE];
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EFI_STATUS Status;
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UINTN TotalSize;
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UINTN VarDataSize;
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UINTN Index;
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UINTN VariableSize;
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UINTN BytesRemaining;
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UINT8 *OffsetPtr;
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VarDataSize = 0;
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//
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// First check if a variable with the given name exists
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//
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Status = VarLibGetVariable (VariableName, VendorGuid, NULL, &VarDataSize, NULL);
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if (Status == EFI_BUFFER_TOO_SMALL) {
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if (*DataSize >= VarDataSize) {
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if (Data == NULL) {
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Status = EFI_INVALID_PARAMETER;
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goto Done;
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}
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DEBUG ((DEBUG_VERBOSE, "GetLargeVariable: Single Variable Found\n"));
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Status = VarLibGetVariable (VariableName, VendorGuid, NULL, DataSize, Data);
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goto Done;
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} else {
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*DataSize = VarDataSize;
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Status = EFI_BUFFER_TOO_SMALL;
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goto Done;
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}
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} else if (Status == EFI_NOT_FOUND) {
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//
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// Check if the first variable of a multi-variable set exists
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//
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if (StrLen (VariableName) >= (MAX_VARIABLE_NAME_SIZE - MAX_VARIABLE_SPLIT_DIGITS)) {
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DEBUG ((DEBUG_ERROR, "GetLargeVariable: Variable name too long\n"));
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Status = EFI_OUT_OF_RESOURCES;
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goto Done;
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}
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VarDataSize = 0;
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Index = 0;
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ZeroMem (TempVariableName, MAX_VARIABLE_NAME_SIZE);
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UnicodeSPrint (TempVariableName, MAX_VARIABLE_NAME_SIZE, L"%s%d", VariableName, Index);
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Status = VarLibGetVariable (TempVariableName, VendorGuid, NULL, &VarDataSize, NULL);
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if (Status == EFI_BUFFER_TOO_SMALL) {
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//
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// The first variable exists. Calculate the total size of all the variables.
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//
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DEBUG ((DEBUG_VERBOSE, "GetLargeVariable: Multiple Variables Found\n"));
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TotalSize = 0;
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for (Index = 0; Index < MAX_VARIABLE_SPLIT; Index++) {
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VarDataSize = 0;
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ZeroMem (TempVariableName, MAX_VARIABLE_NAME_SIZE);
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UnicodeSPrint (TempVariableName, MAX_VARIABLE_NAME_SIZE, L"%s%d", VariableName, Index);
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Status = VarLibGetVariable (TempVariableName, VendorGuid, NULL, &VarDataSize, NULL);
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if (Status != EFI_BUFFER_TOO_SMALL) {
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break;
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}
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TotalSize += VarDataSize;
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}
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DEBUG ((DEBUG_VERBOSE, "TotalSize = %d, NumVariables = %d\n", TotalSize, Index));
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//
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// Check if the user provided a large enough buffer
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//
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if (*DataSize >= TotalSize) {
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if (Data == NULL) {
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Status = EFI_INVALID_PARAMETER;
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goto Done;
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}
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//
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// Read the data from all variables
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//
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OffsetPtr = (UINT8 *) Data;
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BytesRemaining = *DataSize;
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for (Index = 0; Index < MAX_VARIABLE_SPLIT; Index++) {
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VarDataSize = 0;
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ZeroMem (TempVariableName, MAX_VARIABLE_NAME_SIZE);
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UnicodeSPrint (TempVariableName, MAX_VARIABLE_NAME_SIZE, L"%s%d", VariableName, Index);
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VariableSize = BytesRemaining;
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DEBUG ((DEBUG_INFO, "Reading %s, Guid = %g,", TempVariableName, VendorGuid));
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Status = VarLibGetVariable (TempVariableName, VendorGuid, NULL, &VariableSize, (VOID *) OffsetPtr);
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DEBUG ((DEBUG_INFO, " Size %d\n", VariableSize));
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if (EFI_ERROR (Status)) {
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if (Status == EFI_NOT_FOUND) {
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DEBUG ((DEBUG_VERBOSE, "No more variables found\n"));
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Status = EFI_SUCCESS; // The end has been reached
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}
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goto Done;
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}
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if (VariableSize < BytesRemaining) {
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BytesRemaining -= VariableSize;
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OffsetPtr += VariableSize;
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} else {
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DEBUG ((DEBUG_VERBOSE, "All data has been read\n"));
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BytesRemaining = 0;
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break;
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}
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} //End of for loop
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goto Done;
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} else {
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*DataSize = TotalSize;
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Status = EFI_BUFFER_TOO_SMALL;
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goto Done;
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}
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} else {
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Status = EFI_NOT_FOUND;
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}
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}
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Done:
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DEBUG ((DEBUG_ERROR, "GetLargeVariable: Status = %r\n", Status));
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return Status;
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}
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