arch/arm64/imx9: add an ELE-backed /dev/random driver

Documentation/platforms/arm64/imx9/index.rst

@@ -2,6 +2,42 @@
 NXP i.MX9
 =========
 
+Peripheral Support
+==================
+
+==========  =======  =====================================================
+Peripheral  Support  Notes
+==========  =======  =====================================================
+ELE         Yes      EdgeLock Enclave, used for entropy and secure boot
+RNG         Yes      ``/dev/random`` and ``/dev/urandom``, backed by the ELE
+==========  =======  =====================================================
+
+RNG
+---
+
+The EdgeLock Enclave contains a true random number generator. ``CONFIG_IMX9_RNG``
+registers it as ``/dev/random`` and ``/dev/urandom``, which is what seeds the
+kernel entropy pool from hardware. Without it ``up_randompool_initialize()``
+has no hardware source.
+
+``CONFIG_IMX9_RNG`` selects ``CONFIG_IMX9_ELE`` and ``CONFIG_ARCH_HAVE_RNG``.
+``CONFIG_DEV_RANDOM`` then defaults on; ``CONFIG_DEV_URANDOM`` does not and must
+be set explicitly, after which ``CONFIG_DEV_URANDOM_ARCH`` selects the hardware
+backend rather than the software PRNG.
+
+A read is served in blocks, looping until the request is satisfied. Every block
+is checked before it is returned, and a failed check is an error rather than a
+short read: the buffer must have been written by the ELE, must not be all
+zeros, and must differ from the previous block, which is the FIPS 140-2
+continuous test.
+
+.. code-block:: console
+
+   nsh> hexdump /dev/random -c 32
+   /dev/random at 00000000:
+   0000: 7c 9a f9 b0 fb 89 be 9d 23 bf 17 28 88 43 67 10
+   0010: c5 79 10 9e d7 be ca 42 2f 51 00 bd bc ce 77 54
+
 Supported Boards
 ================
 

arch/arm64/src/imx9/CMakeLists.txt

@@ -90,7 +90,15 @@ if(CONFIG_IMX9_FLEXSPI_NOR)
 endif()
 
 if(CONFIG_IMX9_BOOTLOADER)
-  list(APPEND SRCS imx9_system_ctl.c imx9_trdc.c imx9_ele.c)
+  list(APPEND SRCS imx9_system_ctl.c imx9_trdc.c)
+endif()
+
+if(CONFIG_IMX9_ELE)
+  list(APPEND SRCS imx9_ele.c)
+endif()
+
+if(CONFIG_IMX9_RNG)
+  list(APPEND SRCS imx9_rng.c)
 endif()
 
 if(CONFIG_IMX9_ROMAPI)

arch/arm64/src/imx9/Kconfig

@@ -81,6 +81,7 @@ config IMX9_BOOTLOADER
 	bool "Bootloader"
 	select ARM64_DECODEFIQ if ARCH_ARM64_EXCEPTION_LEVEL = 3
 	select IMX9_DDR_TRAINING if ARCH_ARM64_EXCEPTION_LEVEL = 3
+	select IMX9_ELE
 	default n
 	---help---
 		Configure NuttX as the bootloader. NuttX will be compiled
@@ -125,8 +126,22 @@ config IMX_AHAB_CNTR_ADDR
 	---help---
 		Physical address where the AHAB container header is loaded into memory.
 
+config IMX9_ELE
+	bool
+	default n
+
 menu "i.MX9 Peripheral Selection"
 
+config IMX9_RNG
+	bool "ELE true random number generator"
+	default n
+	select IMX9_ELE
+	select ARCH_HAVE_RNG
+	---help---
+		Register /dev/random and /dev/urandom, both backed by the ELE
+		true random number generator. Without this the entropy pool is
+		never seeded from hardware.
+
 config IMX9_EDMA
 	bool "eDMA"
 	default n

arch/arm64/src/imx9/Make.defs

@@ -103,9 +103,16 @@ endif
 ifeq ($(CONFIG_IMX9_BOOTLOADER),y)
   CHIP_CSRCS += imx9_system_ctl.c
   CHIP_CSRCS += imx9_trdc.c
+endif
+
+ifeq ($(CONFIG_IMX9_ELE),y)
   CHIP_CSRCS += imx9_ele.c
 endif
 
+ifeq ($(CONFIG_IMX9_RNG),y)
+  CHIP_CSRCS += imx9_rng.c
+endif
+
 ifeq ($(CONFIG_IMX9_ROMAPI),y)
   CHIP_CSRCS += imx9_romapi.c
 endif

arch/arm64/src/imx9/imx9_ele.c

@@ -24,6 +24,7 @@
  * Included Files
  ****************************************************************************/
 
+#include <nuttx/arch.h>
 #include <nuttx/debug.h>
 #include <errno.h>
 
@@ -146,6 +147,30 @@ static void imx9_ele_receivemsg(struct ele_msg *msg_ptr)
     }
 }
 
+/****************************************************************************
+ * Name: imx9_ele_buffer_pa
+ *
+ * Description:
+ *   Physical address of a buffer the ELE will read or write.  The enclave
+ *   addresses memory physically while cache maintenance takes the virtual
+ *   address, so a caller holding one of them cannot supply the other.
+ *
+ * Returned Value:
+ *   The physical address, or zero if the buffer is not mapped.
+ *
+ ****************************************************************************/
+
+static uintptr_t imx9_ele_buffer_pa(void *va)
+{
+#ifdef CONFIG_ARCH_USE_MMU
+  return up_addrenv_va_to_pa(va);
+#else
+  /* Without translation the virtual address is the physical one. */
+
+  return (uintptr_t)va;
+#endif
+}
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -199,6 +224,9 @@ uint32_t imx9_ele_read_common_fuse(uint32_t fuse_id)
 int imx9_ele_get_key(uint8_t *key, size_t key_size,
                      uint8_t *ctx, size_t ctx_size)
 {
+  uintptr_t key_pa;
+  uintptr_t ctx_pa;
+
   if (!key)
     {
       _err("Invalid key parameter\n");
@@ -229,17 +257,27 @@ int imx9_ele_get_key(uint8_t *key, size_t key_size,
       return -EINVAL;
     }
 
+  key_pa = imx9_ele_buffer_pa(key);
+  ctx_pa = imx9_ele_buffer_pa(ctx);
+
+  if (key_pa == 0 || ctx_pa == 0)
+    {
+      _err("Buffer is not mapped\n");
+      return -EFAULT;
+    }
+
   msg.header.version = ELE_VERSION;
   msg.header.tag = ELE_CMD_TAG;
   msg.header.size = 7;
   msg.header.command = ELE_DERIVE_KEY_REQ;
-  msg.data[0] = upper_32_bits((ulong)key);
-  msg.data[1] = lower_32_bits((ulong)key);
-  msg.data[2] = upper_32_bits((ulong)ctx);
-  msg.data[3] = lower_32_bits((ulong)ctx);
+  msg.data[0] = upper_32_bits((ulong)key_pa);
+  msg.data[1] = lower_32_bits((ulong)key_pa);
+  msg.data[2] = upper_32_bits((ulong)ctx_pa);
+  msg.data[3] = lower_32_bits((ulong)ctx_pa);
   msg.data[4] = ((ctx_size << 16) | key_size);
 
   uint32_t crc = msg.header.data;
+
   for (uint32_t i = 0; i < msg.header.size - 2; i++)
     {
       crc ^= msg.data[i];
@@ -424,6 +462,7 @@ int imx9_ele_get_trng_state(void)
     {
       struct ele_trng_state *ele_trng =
         (struct ele_trng_state *)(msg.data + 1);
+
       if (ele_trng->trng_state != ELE_TRNG_STATUS_READY ||
           ele_trng->csal_state != ELE_CSAL_STATUS_READY)
         {
@@ -442,17 +481,39 @@ int imx9_ele_get_trng_state(void)
   return -EIO;
 }
 
-int imx9_ele_get_random(uint32_t paddr, size_t len)
+int imx9_ele_get_random(void *buf, size_t len)
 {
   uint16_t counter = 0;
   uint16_t max_tries = ELE_RNG_TIMEOUT_US / ELE_RNG_SLEEP_US;
+  uintptr_t paddr;
 
-  if (paddr == 0 || len == 0)
+  if (buf == NULL || len == 0)
     {
       _err("Wrong input parameters!\n");
       return -EINVAL;
     }
 
+  /* The buffer is invalidated after the transfer, so anything sharing its
+   * first or last cache line would lose whatever was written meanwhile.
+   */
+
+  if (!IS_ALIGNED((uintptr_t)buf, ARMV8A_DCACHE_LINESIZE) ||
+      !IS_ALIGNED(len, ARMV8A_DCACHE_LINESIZE))
+    {
+      _err("Buffer is not a whole number of cache lines\n");
+      return -EINVAL;
+    }
+
+  paddr = imx9_ele_buffer_pa(buf);
+
+  /* The address travels in a single 32-bit message word. */
+
+  if (paddr == 0 || paddr > UINT32_MAX - len)
+    {
+      _err("Buffer is not mapped, or is beyond the ELE address range\n");
+      return -EFAULT;
+    }
+
   while ((imx9_ele_get_trng_state() != 0))
     {
       if (counter > max_tries)
@@ -465,16 +526,18 @@ int imx9_ele_get_random(uint32_t paddr, size_t len)
       counter++;
     }
 
-  /* Flush the cache before sending the request to ELE. */
+  /* Cache maintenance takes the virtual address; the ELE takes the
+   * physical one.
+   */
 
-  up_flush_dcache((uintptr_t)paddr, (uintptr_t)(paddr + len));
+  up_flush_dcache((uintptr_t)buf, (uintptr_t)buf + len);
 
   msg.header.version = ELE_VERSION_FW;
   msg.header.tag = ELE_CMD_TAG;
   msg.header.size = 4;
   msg.header.command = ELE_GET_RNG_REQ;
   msg.data[0] = 0;
-  msg.data[1] = paddr;
+  msg.data[1] = (uint32_t)paddr;
   msg.data[2] = len;
 
   imx9_ele_sendmsg(&msg);
@@ -484,8 +547,7 @@ int imx9_ele_get_random(uint32_t paddr, size_t len)
     {
       /* Invalidate the cache so we can read the result from RAM. */
 
-      up_invalidate_dcache((uintptr_t)paddr,
-                           (uintptr_t)(paddr + len));
+      up_invalidate_dcache((uintptr_t)buf, (uintptr_t)buf + len);
       return 0;
     }
 

arch/arm64/src/imx9/imx9_ele.h

@@ -266,7 +266,7 @@ int imx9_ele_get_trng_state(void);
  *
  ****************************************************************************/
 
-int imx9_ele_get_random(uint32_t paddr, size_t len);
+int imx9_ele_get_random(void *buf, size_t len);
 
 /****************************************************************************
  * Name: imx9_ele_commit