Implement BlGetRandomValue() and BlInitializeEntropy() routines for future KASLR support

sdk/xtdk/bltypes.h

@@ -68,8 +68,10 @@ typedef EFI_STATUS (*PBL_GET_CONFIGURATION_TABLE)(IN PEFI_GUID TableGuid, OUT PV
 typedef VOID (*PBL_GET_MAPPINGS_COUNT)(IN PXTBL_PAGE_MAPPING PageMap, OUT PULONG NumberOfMappings);
 typedef EFI_STATUS (*PBL_GET_MEMORY_MAP)(OUT PEFI_MEMORY_MAP MemoryMap);
 typedef PLIST_ENTRY (*PBL_GET_MODULES_LIST)();
+typedef ULONGLONG (*PBL_GET_RANDOM_VALUE)(IN OUT PULONGLONG RNGBuffer);
 typedef INT_PTR (*PBL_GET_SECURE_BOOT_STATUS)();
 typedef PVOID (*PBL_GET_VIRTUAL_ADDRESS)(IN PXTBL_PAGE_MAPPING PageMap, IN PVOID PhysicalAddress);
+typedef EFI_STATUS (*PBL_INITIALIZE_ENTROPY)(PULONGLONG RNGBuffer);
 typedef VOID (*PBL_INITIALIZE_PAGE_MAP)(OUT PXTBL_PAGE_MAPPING PageMap, IN SHORT PageMapLevel, IN PAGE_SIZE PageSize);
 typedef EFI_STATUS (*PBL_INSTALL_XT_PROTOCOL)(IN PVOID Interface, IN PEFI_GUID Guid);
 typedef EFI_STATUS (*PBL_INVOKE_BOOT_PROTOCOL)(IN PLIST_ENTRY OptionsList);
@@ -375,7 +377,9 @@ typedef struct _XTBL_LOADER_PROTOCOL
     {
         PBL_EXIT_BOOT_SERVICES ExitBootServices;
         PBL_GET_CONFIGURATION_TABLE GetConfigurationTable;
+        PBL_GET_RANDOM_VALUE GetRandomValue;
         PBL_GET_SECURE_BOOT_STATUS GetSecureBootStatus;
+        PBL_INITIALIZE_ENTROPY InitializeEntropy;
         PBL_LOAD_EFI_IMAGE LoadEfiImage;
         PBL_POWER_SYSTEM RebootSystem;
         PBL_POWER_SYSTEM ShutdownSystem;

xtldr/efiutils.c

@@ -103,6 +103,31 @@ BlGetConfigurationTable(IN PEFI_GUID TableGuid,
     return STATUS_EFI_NOT_FOUND;
 }
 
+/**
+ * Returns a random value based on the initialized RNG buffer.
+ *
+ * @param RNGBuffer
+ *        Supplies a pointer to the RNG buffer.
+ *
+ * @return This routine returns a random value.
+ *
+ * @since XT 1.0
+ *
+ * @see https://en.wikipedia.org/wiki/Xorshift
+ */
+XTCDECL
+ULONGLONG
+BlGetRandomValue(IN OUT PULONGLONG RNGBuffer)
+{
+    /* Recalculate RNG buffer with XORSHIFT */
+    *RNGBuffer ^= *RNGBuffer >> 12;
+    *RNGBuffer ^= *RNGBuffer << 25;
+    *RNGBuffer ^= *RNGBuffer >> 27;
+
+    /* Return random value */
+    return *RNGBuffer * 0x2545F4914F6CDD1D;
+}
+
 /**
  * Checks whether SecureBoot is enabled or not.
  *
@@ -136,6 +161,50 @@ BlGetSecureBootStatus()
     return SecureBootStatus;
 }
 
+/**
+ * Initializes the RNG buffer with random bytes from the default EFI RNG algorithm.
+ *
+ * @param RNGBuffer
+ *        Supplies a pointer to the RNG buffer.
+ *
+ * @return This routine returns a status code.
+ *
+ * @since XT 1.0
+ */
+XTCDECL
+EFI_STATUS
+BlInitializeEntropy(PULONGLONG RNGBuffer)
+{
+    EFI_GUID RngGuid = EFI_RNG_PROTOCOL_GUID;
+    PEFI_RNG_PROTOCOL Rng;
+    EFI_STATUS Status;
+    ULONGLONG Seed;
+
+    /* Initialize variables */
+    Rng = NULL;
+    Seed = 0;
+
+    /* Locate RNG protocol */
+    Status = EfiSystemTable->BootServices->LocateProtocol(&RngGuid, NULL, (PVOID *)&Rng);
+    if(Status != STATUS_EFI_SUCCESS)
+    {
+        /* Failed to locate RNG protocol, return status code */
+        return Status;
+    }
+
+    /* Get RNG value using the default algorithm */
+    Status = Rng->GetRNG(Rng, NULL, 8, (PUCHAR)&Seed);
+    if(Status != STATUS_EFI_SUCCESS)
+    {
+        /* Failed to get RNG value, return status code */
+        return Status;
+    }
+
+    /* Initialize RNG state and return success */
+    *RNGBuffer = Seed ? Seed : 1;
+    return STATUS_EFI_SUCCESS;
+}
+
 /**
  * Loads an EFI image into memory.
  *

xtldr/includes/xtldr.h

@@ -150,6 +150,10 @@ XTCDECL
 PLIST_ENTRY
 BlGetModulesList();
 
+XTCDECL
+ULONGLONG
+BlGetRandomValue(IN OUT PULONGLONG RNGBuffer);
+
 XTCDECL
 INT_PTR
 BlGetSecureBootStatus();
@@ -180,6 +184,10 @@ XTCDECL
 VOID
 BlInitializeConsole();
 
+XTCDECL
+EFI_STATUS
+BlInitializeEntropy(PULONGLONG RNGBuffer);
+
 XTCDECL
 VOID
 BlInitializePageMap(OUT PXTBL_PAGE_MAPPING PageMap,

xtldr/protocol.c

@@ -654,7 +654,9 @@ BlpInstallXtLoaderProtocol()
     BlpLdrProtocol.Tui.UpdateProgressBar = BlUpdateProgressBar;
     BlpLdrProtocol.Util.ExitBootServices = BlExitBootServices;
     BlpLdrProtocol.Util.GetConfigurationTable = BlGetConfigurationTable;
+    BlpLdrProtocol.Util.GetRandomValue = BlGetRandomValue;
     BlpLdrProtocol.Util.GetSecureBootStatus = BlGetSecureBootStatus;
+    BlpLdrProtocol.Util.InitializeEntropy = BlInitializeEntropy;
     BlpLdrProtocol.Util.LoadEfiImage = BlLoadEfiImage;
     BlpLdrProtocol.Util.RebootSystem = BlRebootSystem;
     BlpLdrProtocol.Util.ShutdownSystem = BlShutdownSystem;