nvram.c

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#include <windows.h>
 
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>
 
/* Boilerplate asking privileges to write to the nvram's efi store. */
void obtain_privilege() {
  HANDLE hToken;
  TOKEN_PRIVILEGES tkp;
 
  OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken);
  LookupPrivilegeValue(NULL, SE_SYSTEM_ENVIRONMENT_NAME, &tkp.Privileges[0].Luid);
  tkp.PrivilegeCount = 1;
  tkp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
  AdjustTokenPrivileges(hToken, FALSE, &tkp, 0, (PTOKEN_PRIVILEGES)NULL, 0);
}
 
int main(int argc, char *argv[]) {
  if (argc < 2) {
    printf("Usage:\n  nvram var\n  nvram var value\n");
    return -1;
  }
 
  const char *variable = argv[1];
  const char *guid = "{7C436110-AB2A-4BBB-A880-FE41995C9F82}";
  int code = EXIT_SUCCESS;
 
  obtain_privilege();
 
  if (argc == 2) {
    char readValue[256] = {0};
    uint32_t readValueSize = GetFirmwareEnvironmentVariableA(
      variable, guid, readValue, sizeof(readValue)-1);
    if (readValueSize > 0) {
      printf("%s = %s\n", variable, readValue);
    } else {
      printf("Failed to read %s, code %u\n",
        variable, (unsigned)GetLastError());
      code = EXIT_FAILURE;
    }
  } else {
    bool ok = SetFirmwareEnvironmentVariableA(
      variable, guid, argv[2], strlen(argv[2]));
    if (ok) {
      printf("%s was set to %s\n", variable, argv[2]);
    } else {
      printf("Failed to set %s to %s, code %u\n",
        variable, argv[2], (unsigned)GetLastError());
      code = EXIT_FAILURE;
    }
  }
 
  return code;
}