Replacement for Boot ROM aes_unwrap

cores/esp8266/aes_unwrap.cpp

@@ -0,0 +1,165 @@
+/*
+ *  Replacement for the ROM aes_unwrap() function. It uses the heap instead of
+ *  the static DRAM address at 0x3FFFEA80, which may step on the SYS stack in
+ *  special circumstances such as HWDT Stack Dump.
+ *
+ *  When not using WPS, the address space 0x3FFFE000 up to 0x40000000 is mostly
+ *  available for the stacks. The one known exception is the ROM AES APIs. When
+ *  `aes_decrypt_init` is called, it uses memory at 0x3FFFEA80 up to 0x3FFFEB30
+ *  for a buffer. At the finish, `aes_decrypt_deinit` zeros out the buffer.
+ *
+ *  The NONOS SDK appears to have replacements for most of the ROM's AES APIs.
+ *  However, the SDK still calls on the ROM's aes_unwrap function, which uses
+ *  the ROM's AES APIs to operate. These calls can overwrite some of the stack
+ *  space. To resolve the problem, this module replaces `aes_unwrap`.
+ *
+ *  Final note, so far, I have not seen a problem when using the extra 4K heap
+ *  option without the "debug HWDT". It is when combined with the HWDT Stack
+ *  Dump that a problem shows. This combination adds a Boot ROM stack, which
+ *  pushes up the SYS and CONT stacks into the AES Buffer space. Then the
+ *  problem shows.
+ *
+ *  While debugging with painted stack space, during WiFi Connect, Reconnect,
+ *  and about every hour, a block of memory 0x3FFFEA80 - 0x3FFFEB30 (176 bytes)
+ *  was zeroed by the Boot ROM function aes_decrypt_init. All other painted
+ *  memory in the area was untouched after starting WiFi.
+ */
+
+#if defined(KEEP_ROM_AES_UNWRAP)
+// Using the ROM version of aes_unwrap should be fine for the no extra 4K case
+// which is usually used in conjunction with WPS.
+
+#else
+// This is required for DEBUG_ESP_HWDT.
+// The need is unconfirmed for the extra 4K heap case.
+#include "umm_malloc/umm_malloc.h"
+
+extern "C" {
+
+// Uses this function from the Boot ROM
+void rijndaelKeySetupDec(u32 rk[], const u8 cipherKey[]);
+
+// This replaces the Boot ROM version just for this module
+// Uses a malloc-ed buffer instead of the static buffer in stack address space.
+static void *aes_decrypt_init(const u8 *key, size_t len) {
+  if (16u != len) {
+    return 0;
+  }
+  u32 *rk = (u32 *)malloc(16*11);
+  // u32 *rk = (u32 *)0x3FFFEA80u;    // This is what the ROM would have used.
+  if (rk) {
+    rijndaelKeySetupDec(rk, key);
+  }
+  return (void *)rk;
+}
+
+// This replaces the Boot ROM version just for this module
+static void aes_decrypt_deinit(void *ctx) {
+  if (ctx) {
+    ets_memset(ctx, 0, 16*11);
+    if ((uint32_t)ctx != 0x3FFFEA80ul) {
+      free(ctx);
+    }
+  }
+  return;
+}
+
+/*
+ * The NONOS SDK has an override on this function. To replace the aes_unwrap
+ * without changing its behavior too much. We need access to the ROM version of
+ * the AES APIs to make our aes_unwrap functionally equal to the current
+ * environment except for the AES Buffer.
+ */
+#ifndef ROM_aes_decrypt
+#define ROM_aes_decrypt         0x400092d4
+#endif
+
+typedef void  (*fp_aes_decrypt_t)(void *ctx, const u8 *crypt, u8 *plain);
+#define AES_DECRYPT (reinterpret_cast<fp_aes_decrypt_t>(ROM_aes_decrypt))
+
+///////////////////////////////////////////////////////////////////////////////
+///////////////////////////////////////////////////////////////////////////////
+///////////////////////////////////////////////////////////////////////////////
+/*
+ * This aes_unwrap() function overrides/replaces the Boot ROM version.
+ *
+ * It was adapted from aes_unwrap() found in the ESP8266 RTOS SDK
+ *   .../components/wap_supplicant/src/crypto/aes-unwrap.c
+ *
+ */
+///////////////////////////////////////////////////////////////////////////////
+/*
+ * AES key unwrap (128-bit KEK, RFC3394)
+ *
+ * Copyright (c) 2003-2007, Jouni Malinen <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Alternatively, this software may be distributed under the terms of BSD
+ * license.
+ *
+ * See README and COPYING for more details.
+ */
+
+/**  based on RTOS SDK
+ * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
+ * @kek: Key encryption key (KEK)
+ * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
+ * bytes
+ * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
+ * @plain: Plaintext key, n * 64 bits
+ * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
+ */
+int aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
+{
+	u8 a[8], *r, b[16];
+	int i, j;
+	void *ctx;
+
+	/* 1) Initialize variables. */
+	ets_memcpy(a, cipher, 8);
+	r = plain;
+	ets_memcpy(r, cipher + 8, 8 * n);
+
+	ctx = aes_decrypt_init(kek, 16);
+	if (ctx == NULL)
+		return -1;
+
+	/* 2) Compute intermediate values.
+	 * For j = 5 to 0
+	 *     For i = n to 1
+	 *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
+	 *         A = MSB(64, B)
+	 *         R[i] = LSB(64, B)
+	 */
+	for (j = 5; j >= 0; j--) {
+		r = plain + (n - 1) * 8;
+		for (i = n; i >= 1; i--) {
+			ets_memcpy(b, a, 8);
+			b[7] ^= n * j + i;
+
+			ets_memcpy(b + 8, r, 8);
+			AES_DECRYPT(ctx, b, b);
+			ets_memcpy(a, b, 8);
+			ets_memcpy(r, b + 8, 8);
+			r -= 8;
+		}
+	}
+	aes_decrypt_deinit(ctx);
+
+	/* 3) Output results.
+	 *
+	 * These are already in @plain due to the location of temporary
+	 * variables. Just verify that the IV matches with the expected value.
+	 */
+	for (i = 0; i < 8; i++) {
+		if (a[i] != 0xa6)
+			return -1;
+	}
+
+	return 0;
+}
+};
+#endif