bootloader: self lock at the end of execution

Disables read and execute on memory containing NSIB
right before jumping to application.

Signed-off-by: Mateusz Michalek <mateusz.michalek@nordicsemi.no>

Author: michalek-no

subsys/bootloader/Kconfig

@@ -104,6 +104,13 @@ config SB_CLEANUP_RAM
 	help
 	  Sets contents of memory to 0 before jumping to application.
 
+config SB_DISABLE_SELF_RWX
+	bool "Disable read and execution on self NVM"
+	depends on SOC_NRF54L15_CPUAPP && !FPROTECT_ALLOW_COMBINED_REGIONS
+	help
+	  Sets RRAMC's BOOTCONF region protection before jumping to application.
+	  It disables reads writes and execution memory area which holds NSIB.
+
 endif # IS_SECURE_BOOTLOADER
 
 config IS_BOOTLOADER_IMG

subsys/bootloader/bl_boot/bl_boot.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020 Nordic Semiconductor ASA
+ * Copyright (c) 2020-2025 Nordic Semiconductor ASA
  *
  * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
  */
@@ -19,6 +19,25 @@
 #include <hal/nrf_gpio.h>
 #endif
 
+#if defined(CONFIG_SB_DISABLE_SELF_RWX)
+/* Disabling R_X has to be done while running from RAM for obvious reasons.
+ * Moreover as a last step before jumping to application it must work even after
+ * RAM has been cleared, therefore we are using custom RAM function relocator.
+ * This relocator runs after RAM cleanup.
+ * Size of the relocated 'locking' function isn't known but it doesn't matter
+ * as long as at least entire aforementioned function is copied to RAM.
+ */
+#include <hal/nrf_rramc.h>
+
+#define FUNCTION_BUFFER_LEN 64
+#define RRAMC_REGION_RWX_LSB 0
+#define RRAMC_REGION_RWX_WIDTH 3
+#define RRAMC_REGION_TO_LOCK_ADDR NRF_RRAMC->REGION[3].CONFIG
+#define RRAMC_REGION_TO_LOCK_ADDR_H (((uint32_t)(&(RRAMC_REGION_TO_LOCK_ADDR))) >> 16)
+#define RRAMC_REGION_TO_LOCK_ADDR_L (((uint32_t)(&(RRAMC_REGION_TO_LOCK_ADDR))) & 0x0000fffful)
+static uint8_t ram_exec_buf[FUNCTION_BUFFER_LEN];
+#endif /* CONFIG_SB_DISABLE_SELF_RWX */
+
 #ifdef CONFIG_UART_NRFX_UARTE
 static void uninit_used_uarte(NRF_UARTE_Type *p_reg)
 {
@@ -151,39 +170,100 @@ void bl_boot(const struct fw_info *fw_info)
 	__set_PSPLIM(0);
 	__set_MSPLIM(0);
 #endif
-
 	/* Set MSP to the new address and clear any information from PSP */
 	__set_MSP(vector_table[0]);
 	__set_PSP(0);
 
-#if CONFIG_SB_CLEANUP_RAM
 	__asm__ volatile (
 		/* vector_table[1] -> r0 */
-		"   mov r0, %0\n"
+		"   mov  r0, %0\n"
+#ifdef CONFIG_SB_CLEANUP_RAM
 		/* Base to write -> r1 */
-		"   mov r1, %1\n"
+		"   mov  r1, %1\n"
 		/* Size to write -> r2 */
-		"   mov r2, %2\n"
+		"   mov  r2, %2\n"
 		/* Value to write -> r3 */
-		"   mov r3, %3\n"
+		"   movw r3, %3\n"
 		"clear:\n"
-		"   str r3, [r1]\n"
-		"   add r1, r1, #4\n"
-		"   sub r2, r2, #4\n"
-		"   cbz r2, out\n"
-		"   b   clear\n"
+		"   str  r3, [r1]\n"
+		"   add  r1, r1, #4\n"
+		"   sub  r2, r2, #4\n"
+		"   cbz  r2, out\n"
+		"   b    clear\n"
 		"out:\n"
 		"   dsb\n"
+#endif /* CONFIG_SB_CLEANUP_RAM */
+
+#ifdef CONFIG_SB_DISABLE_SELF_RWX
+		/* FUNCTION_BUFFER_LEN */
+		"   movw r4, %4\n"
+		/* Address of ram_exec_buf goes to r2 */
+		"   mov  r2, %5\n"
+		"   movw r3, :lower16:bootconf_disable_rwx\n"
+		"   movt r3, :upper16:bootconf_disable_rwx\n"
+		/* Adjust address for thumb */
+		"   and  r3, #0xfffffffe\n"
+		/* Address of ram_exec_buf also goes to r5 */
+		"   mov  r5, %5\n"
+		/* Adjust buffer address for thumb */
+		"   orr  r5, #0x1\n"
+		/* End of the copy address in r4 */
+		"   add  r4, r2\n"
+		"ram_cpy:\n"
+		/* Read and increment */
+		"   ldrb r1, [r3], #1\n"
+		/* Write and increment */
+		"   strb r1, [r2], #1\n"
+		/* Check if end address is reached */
+		"   cmp  r2, r4\n"
+		"   bne  ram_cpy\n"
+		"   dsb\n"
+		/* Jump to ram */
+		"   bx   r5\n"
+		/* CODE_UNREACHABLE */
+
+		".thumb_func\n"
+		"bootconf_disable_rwx:\n"
+		"   movw r1, %6\n"
+		"   movt r1, %7\n"
+		"   ldr  r2, [r1]\n"
+		/* Size of the region should be set at this point
+		 * by provisioning through BOOTCONF.
+		 * If not, set it according partition size.
+		 */
+		"   ands r4, r2, %12\n"
+		"   cbnz r4, clear_rwx\n"
+		"   movt r2, %8\n"
+		"clear_rwx:\n"
+		"   bfc  r2, %9, %10\n"
+		/* Disallow further modifications */
+		"   orr  r2, %11\n"
+		"   str  r2, [r1]\n"
+		"   dsb\n"
+		/* Next assembly line is important for current function */
+
+#endif /* CONFIG_SB_DISABLE_SELF_RWX */
+
 		/* Jump to reset vector of an app */
-		"   bx r0\n"
+		"   bx   r0\n"
 		:
-		: "r" (vector_table[1]), "i" (CONFIG_SRAM_BASE_ADDRESS),
-		  "i" (CONFIG_SRAM_SIZE * 1024), "i" (0)
-		: "r0", "r1", "r2", "r3", "memory"
+		: "r" (vector_table[1]),
+		  "i" (CONFIG_SRAM_BASE_ADDRESS),
+		  "i" (CONFIG_SRAM_SIZE * 1024),
+		  "i" (0)
+#ifdef CONFIG_SB_DISABLE_SELF_RWX
+		  , "i" (FUNCTION_BUFFER_LEN),
+		  "r" (ram_exec_buf),
+		  "i" (RRAMC_REGION_TO_LOCK_ADDR_L),
+		  "i" (RRAMC_REGION_TO_LOCK_ADDR_H),
+		  "i" (CONFIG_PM_PARTITION_SIZE_B0_IMAGE / 1024),
+		  "i" (RRAMC_REGION_RWX_LSB),
+		  "i" (RRAMC_REGION_RWX_WIDTH),
+		  "i" (RRAMC_REGION_CONFIG_LOCK_Msk),
+		  "i" (RRAMC_REGION_CONFIG_SIZE_Msk)
+#endif /* CONFIG_SB_DISABLE_SELF_RWX */
+		: "r0", "r1", "r2", "r3", "r4", "r5", "memory"
 	);
-#else
-	/* Call reset handler. */
-	((void (*)(void))vector_table[1])();
-#endif
+
 	CODE_UNREACHABLE;
 }