[efi] Use the EFI_RNG_PROTOCOL as an entropy source if available

Entropy gathering via timer ticks is slow under UEFI (of the order of
20-30 seconds on some machines).  Use the EFI_RNG_PROTOCOL if
available, to speed up the process of entropy gathering.

Note that some implementations (including EDK2) will fail if we
request fewer than 32 random bytes at a time, and that the RNG
protocol provides no guarantees about the amount of entropy provided
by a call to GetRNG().  We take the (hopefully pessimistic) view that
a 32-byte block returned by GetRNG() will contain at least the 1.3
bits of entropy claimed by min_entropy_per_sample().

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/interface/efi/efi_entropy.c

@@ -25,7 +25,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <errno.h>
 #include <ipxe/entropy.h>
+#include <ipxe/crc32.h>
 #include <ipxe/efi/efi.h>
+#include <ipxe/efi/Protocol/Rng.h>
 
 /** @file
  *
@@ -33,6 +35,23 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
+/** Random number generator protocol */
+static EFI_RNG_PROTOCOL *efirng;
+EFI_REQUEST_PROTOCOL ( EFI_RNG_PROTOCOL, &efirng );
+
+/** Minimum number of bytes to request from RNG
+ *
+ * The UEFI spec states (for no apparently good reason) that "When a
+ * Deterministic Random Bit Generator (DRBG) is used on the output of
+ * a (raw) entropy source, its security level must be at least 256
+ * bits."  The EDK2 codebase (mis)interprets this to mean that the
+ * call to GetRNG() should fail if given a buffer less than 32 bytes.
+ *
+ * Incidentally, nothing in the EFI RNG protocol provides any way to
+ * report the actual amount of entropy returned by GetRNG().
+ */
+#define EFI_ENTROPY_RNG_LEN 32
+
 /** Time (in 100ns units) to delay waiting for timer tick
  *
  * In theory, UEFI allows us to specify a trigger time of zero to
@@ -56,6 +75,9 @@ static int efi_entropy_enable ( void ) {
 	EFI_STATUS efirc;
 	int rc;
 
+	DBGC ( &tick, "ENTROPY %s RNG protocol\n",
+	       ( efirng ? "has" : "has no" ) );
+
 	/* Create timer tick event */
 	if ( ( efirc = bs->CreateEvent ( EVT_TIMER, TPL_NOTIFY, NULL, NULL,
 					 &tick ) ) != 0 ) {
@@ -80,7 +102,7 @@ static void efi_entropy_disable ( void ) {
 }
 
 /**
- * Wait for an RTC tick
+ * Wait for a timer tick
  *
  * @ret low		TSC low-order bits, or negative error
  */
@@ -114,12 +136,12 @@ static int efi_entropy_tick ( void ) {
 }
 
 /**
- * Get noise sample
+ * Get noise sample from timer ticks
  *
  * @ret noise		Noise sample
  * @ret rc		Return status code
  */
-static int efi_get_noise ( noise_sample_t *noise ) {
+static int efi_get_noise_ticks ( noise_sample_t *noise ) {
 	int before;
 	int after;
 	int rc;
@@ -144,6 +166,57 @@ static int efi_get_noise ( noise_sample_t *noise ) {
 	return 0;
 }
 
+/**
+ * Get noise sample from RNG protocol
+ *
+ * @ret noise		Noise sample
+ * @ret rc		Return status code
+ */
+static int efi_get_noise_rng ( noise_sample_t *noise ) {
+	uint8_t buf[EFI_ENTROPY_RNG_LEN];
+	EFI_STATUS efirc;
+	int rc;
+
+	/* Fail if we have no EFI RNG protocol */
+	if ( ! efirng )
+		return -ENOTSUP;
+
+	/* Get the minimum allowed number of random bytes */
+	if ( ( efirc = efirng->GetRNG ( efirng, NULL, EFI_ENTROPY_RNG_LEN,
+					buf ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( &tick, "ENTROPY could not read from RNG: %s\n",
+		       strerror ( rc ) );
+		return rc;
+	}
+
+	/* Reduce random bytes to a single noise sample.  This seems
+	 * like overkill, but we have no way of knowing how much
+	 * entropy is actually present in the bytes returned by the
+	 * RNG protocol.
+	 */
+	*noise = crc32_le ( 0, buf, sizeof ( buf ) );
+
+	return 0;
+}
+
+/**
+ * Get noise sample
+ *
+ * @ret noise		Noise sample
+ * @ret rc		Return status code
+ */
+static int efi_get_noise ( noise_sample_t *noise ) {
+	int rc;
+
+	/* Try RNG first, falling back to timer ticks */
+	if ( ( ( rc = efi_get_noise_rng ( noise ) ) != 0 ) &&
+	     ( ( rc = efi_get_noise_ticks ( noise ) ) != 0 ) )
+		return rc;
+
+	return 0;
+}
+
 PROVIDE_ENTROPY_INLINE ( efi, min_entropy_per_sample );
 PROVIDE_ENTROPY ( efi, entropy_enable, efi_entropy_enable );
 PROVIDE_ENTROPY ( efi, entropy_disable, efi_entropy_disable );

src/include/ipxe/efi/Protocol/Rng.h

@@ -0,0 +1,158 @@
+/** @file
+  EFI_RNG_PROTOCOL as defined in UEFI 2.4.
+  The UEFI Random Number Generator Protocol is used to provide random bits for use
+  in applications, or entropy for seeding other random number generators.
+
+Copyright (c) 2013, Intel Corporation. All rights reserved.<BR>
+This program and the accompanying materials are licensed and made available under
+the terms and conditions of the BSD License that accompanies this distribution.
+The full text of the license may be found at
+http://opensource.org/licenses/bsd-license.php.
+
+THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#ifndef __EFI_RNG_PROTOCOL_H__
+#define __EFI_RNG_PROTOCOL_H__
+
+FILE_LICENCE ( BSD3 );
+
+///
+/// Global ID for the Random Number Generator Protocol
+///
+#define EFI_RNG_PROTOCOL_GUID \
+  { \
+    0x3152bca5, 0xeade, 0x433d, {0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44 } \
+  }
+
+typedef struct _EFI_RNG_PROTOCOL EFI_RNG_PROTOCOL;
+
+///
+/// A selection of EFI_RNG_PROTOCOL algorithms.
+/// The algorithms listed are optional, not meant to be exhaustive and be argmented by
+/// vendors or other industry standards.
+///
+
+typedef EFI_GUID EFI_RNG_ALGORITHM;
+
+///
+/// The algorithms corresponds to SP800-90 as defined in
+/// NIST SP 800-90, "Recommendation for Random Number Generation Using Deterministic Random
+/// Bit Generators", March 2007.
+///
+#define EFI_RNG_ALGORITHM_SP800_90_HASH_256_GUID \
+  { \
+    0xa7af67cb, 0x603b, 0x4d42, {0xba, 0x21, 0x70, 0xbf, 0xb6, 0x29, 0x3f, 0x96 } \
+  }
+#define EFI_RNG_ALGORITHM_SP800_90_HMAC_256_GUID \
+  { \
+    0xc5149b43, 0xae85, 0x4f53, {0x99, 0x82, 0xb9, 0x43, 0x35, 0xd3, 0xa9, 0xe7 } \
+  }
+#define EFI_RNG_ALGORITHM_SP800_90_CTR_256_GUID \
+  { \
+    0x44f0de6e, 0x4d8c, 0x4045, {0xa8, 0xc7, 0x4d, 0xd1, 0x68, 0x85, 0x6b, 0x9e } \
+  }
+///
+/// The algorithms correspond to X9.31 as defined in
+/// NIST, "Recommended Random Number Generator Based on ANSI X9.31 Appendix A.2.4 Using
+/// the 3-Key Triple DES and AES Algorithm", January 2005.
+///
+#define EFI_RNG_ALGORITHM_X9_31_3DES_GUID \
+  { \
+    0x63c4785a, 0xca34, 0x4012, {0xa3, 0xc8, 0x0b, 0x6a, 0x32, 0x4f, 0x55, 0x46 } \
+  }
+#define EFI_RNG_ALGORITHM_X9_31_AES_GUID \
+  { \
+    0xacd03321, 0x777e, 0x4d3d, {0xb1, 0xc8, 0x20, 0xcf, 0xd8, 0x88, 0x20, 0xc9 } \
+  }
+///
+/// The "raw" algorithm, when supported, is intended to provide entropy directly from
+/// the source, without it going through some deterministic random bit generator.
+///
+#define EFI_RNG_ALGORITHM_RAW \
+  { \
+    0xe43176d7, 0xb6e8, 0x4827, {0xb7, 0x84, 0x7f, 0xfd, 0xc4, 0xb6, 0x85, 0x61 } \
+  }
+
+/**
+  Returns information about the random number generation implementation.
+
+  @param[in]     This                 A pointer to the EFI_RNG_PROTOCOL instance.
+  @param[in,out] RNGAlgorithmListSize On input, the size in bytes of RNGAlgorithmList.
+                                      On output with a return code of EFI_SUCCESS, the size
+                                      in bytes of the data returned in RNGAlgorithmList. On output
+                                      with a return code of EFI_BUFFER_TOO_SMALL,
+                                      the size of RNGAlgorithmList required to obtain the list.
+  @param[out] RNGAlgorithmList        A caller-allocated memory buffer filled by the driver
+                                      with one EFI_RNG_ALGORITHM element for each supported
+                                      RNG algorithm. The list must not change across multiple
+                                      calls to the same driver. The first algorithm in the list
+                                      is the default algorithm for the driver.
+
+  @retval EFI_SUCCESS                 The RNG algorithm list was returned successfully.
+  @retval EFI_UNSUPPORTED             The services is not supported by this driver.
+  @retval EFI_DEVICE_ERROR            The list of algorithms could not be retrieved due to a
+                                      hardware or firmware error.
+  @retval EFI_INVALID_PARAMETER       One or more of the parameters are incorrect.
+  @retval EFI_BUFFER_TOO_SMALL        The buffer RNGAlgorithmList is too small to hold the result.
+
+**/
+typedef
+EFI_STATUS
+(EFIAPI *EFI_RNG_GET_INFO) (
+  IN EFI_RNG_PROTOCOL             *This,
+  IN OUT UINTN                    *RNGAlgorithmListSize,
+  OUT EFI_RNG_ALGORITHM           *RNGAlgorithmList
+  );
+
+/**
+  Produces and returns an RNG value using either the default or specified RNG algorithm.
+
+  @param[in]  This                    A pointer to the EFI_RNG_PROTOCOL instance.
+  @param[in]  RNGAlgorithm            A pointer to the EFI_RNG_ALGORITHM that identifies the RNG
+                                      algorithm to use. May be NULL in which case the function will
+                                      use its default RNG algorithm.
+  @param[in]  RNGValueLength          The length in bytes of the memory buffer pointed to by
+                                      RNGValue. The driver shall return exactly this numbers of bytes.
+  @param[out] RNGValue                A caller-allocated memory buffer filled by the driver with the
+                                      resulting RNG value.
+
+  @retval EFI_SUCCESS                 The RNG value was returned successfully.
+  @retval EFI_UNSUPPORTED             The algorithm specified by RNGAlgorithm is not supported by
+                                      this driver.
+  @retval EFI_DEVICE_ERROR            An RNG value could not be retrieved due to a hardware or
+                                      firmware error.
+  @retval EFI_NOT_READY               There is not enough random data available to satisfy the length
+                                      requested by RNGValueLength.
+  @retval EFI_INVALID_PARAMETER       RNGValue is NULL or RNGValueLength is zero.
+
+**/
+typedef
+EFI_STATUS
+(EFIAPI *EFI_RNG_GET_RNG) (
+  IN EFI_RNG_PROTOCOL            *This,
+  IN EFI_RNG_ALGORITHM           *RNGAlgorithm, OPTIONAL
+  IN UINTN                       RNGValueLength,
+  OUT UINT8                      *RNGValue
+  );
+
+///
+/// The Random Number Generator (RNG) protocol provides random bits for use in
+/// applications, or entropy for seeding other random number generators.
+///
+struct _EFI_RNG_PROTOCOL {
+  EFI_RNG_GET_INFO                GetInfo;
+  EFI_RNG_GET_RNG                 GetRNG;
+};
+
+extern EFI_GUID gEfiRngProtocolGuid;
+extern EFI_GUID gEfiRngAlgorithmSp80090Hash256Guid;
+extern EFI_GUID gEfiRngAlgorithmSp80090Hmac256Guid;
+extern EFI_GUID gEfiRngAlgorithmSp80090Ctr256Guid;
+extern EFI_GUID gEfiRngAlgorithmX9313DesGuid;
+extern EFI_GUID gEfiRngAlgorithmX931AesGuid;
+extern EFI_GUID gEfiRngAlgorithmRaw;
+
+#endif