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[nrf noup] boot: zephyr: Disable self RWX #491

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[nrf noup] boot: zephyr: Disable self RWX #491

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7 changes: 7 additions & 0 deletions boot/zephyr/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -472,6 +472,13 @@ config MCUBOOT_CLEANUP_RAM
help
Sets contents of memory to 0 before jumping to application.

config MCUBOOT_DISABLE_SELF_RWX
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Suggested change
config MCUBOOT_DISABLE_SELF_RWX
config NCS_MCUBOOT_DISABLE_SELF_RWX

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We are trying to not conflict noups with anything that may come from upstream.

bool "Disable read and execution on self NVM"
depends on SOC_NRF54L15_CPUAPP && !FPROTECT
help
Sets RRAMC's region no.4 protection before jumping to application.
It disables reads writes and execution memory area which holds MCUBOOT.

config MCUBOOT_INFINITE_LOOP_AFTER_RAM_CLEANUP
bool "Infinite loop after RAM cleanup"
depends on MCUBOOT_CLEANUP_RAM
Expand Down
129 changes: 98 additions & 31 deletions boot/zephyr/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -148,6 +148,25 @@ K_SEM_DEFINE(boot_log_sem, 1, 1);
#include <nrf_cleanup.h>
#endif

#include <zephyr/linker/linker-defs.h>
#define CLEANUP_RAM_GAP_START ((int)__ramfunc_region_start)
#define CLEANUP_RAM_GAP_SIZE ((int) (__ramfunc_end - __ramfunc_region_start))

#if defined(CONFIG_MCUBOOT_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 these operations are performed while executing from RAM.
* RAM cleanup ommits portion of the memory where code lives.
*/
#include <hal/nrf_rramc.h>

#define RRAMC_REGION_RWX_LSB 0
#define RRAMC_REGION_RWX_WIDTH 3
#define RRAMC_REGION_TO_LOCK_ADDR NRF_RRAMC->REGION[4].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)
#endif /* CONFIG_MCUBOOT_DISABLE_SELF_RWX */

BOOT_LOG_MODULE_REGISTER(mcuboot);

void os_heap_init(void);
Expand All @@ -163,6 +182,84 @@ struct arm_vector_table {
uint32_t reset;
};

static void __ramfunc jump_in(uint32_t reset)
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Can we have better name for this?

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Yes, however this is the hardest part. Any suggestions?

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Have you seen names I have invented?

{
__asm__ volatile (
/* reset -> r0 */
" mov r0, %0\n"
#ifdef CONFIG_MCUBOOT_CLEANUP_RAM
/* Base to write -> r1 */
" mov r1, %1\n"
/* Size to write -> r2 */
" mov r2, %2\n"
/* Value to write -> r3 */
" movw r3, %5\n"
/* gap start */
" mov r4, %3\n"
/* gap size */
" mov r5, %4\n"
"clear:\n"
" subs r6, r4, r1\n"
" cbnz r6, skip_gap\n"
" add r1, r5\n"
"skip_gap:\n"
" str r3, [r1]\n"
" add r1, r1, #1\n"
" sub r2, r2, #1\n"
" cbz r2, clear_end\n"
" b clear\n"
"clear_end:\n"
" dsb\n"
#ifdef CONFIG_MCUBOOT_INFINITE_LOOP_AFTER_RAM_CLEANUP
" b clear_end\n"
#endif /*CONFIG_MCUBOOT_INFINITE_LOOP_AFTER_RAM_CLEANUP */
#endif /* CONFIG_MCUBOOT_CLEANUP_RAM */

#ifdef CONFIG_MCUBOOT_DISABLE_SELF_RWX
".thumb_func\n"
"region_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 NSIB's DISABLE_NEXT_W.
* 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_MCUBOOT_DISABLE_SELF_RWX */

/* Jump to reset vector of an app */
" bx r0\n"
:
: "r" (reset),
"r" (CONFIG_SRAM_BASE_ADDRESS),
"i" (CONFIG_SRAM_SIZE * 1024),
"r" (CLEANUP_RAM_GAP_START),
"r" (CLEANUP_RAM_GAP_SIZE),
"i" (0)
#ifdef CONFIG_MCUBOOT_DISABLE_SELF_RWX
, "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_MCUBOOT_DISABLE_SELF_RWX */
: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "memory"
);
}

static void do_boot(struct boot_rsp *rsp)
{
/* vt is static as it shall not land on the stack,
Expand Down Expand Up @@ -276,37 +373,7 @@ static void do_boot(struct boot_rsp *rsp)
__set_CONTROL(0x00); /* application will configures core on its own */
__ISB();
#endif
#if CONFIG_MCUBOOT_CLEANUP_RAM
__asm__ volatile (
/* vt->reset -> r0 */
" mov r0, %0\n"
/* base to write -> r1 */
" mov r1, %1\n"
/* size to write -> r2 */
" mov r2, %2\n"
/* value to write -> r3 */
" mov 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"
"out:\n"
" dsb\n"
#if CONFIG_MCUBOOT_INFINITE_LOOP_AFTER_RAM_CLEANUP
" b out\n"
#endif /*CONFIG_MCUBOOT_INFINITE_LOOP_AFTER_RAM_CLEANUP */
/* jump to reset vector of an app */
" bx r0\n"
:
: "r" (vt->reset), "i" (CONFIG_SRAM_BASE_ADDRESS),
"i" (CONFIG_SRAM_SIZE * 1024), "i" (0)
: "r0", "r1", "r2", "r3", "memory"
);
#else
((void (*)(void))vt->reset)();
#endif
jump_in(vt->reset);
}

#elif defined(CONFIG_XTENSA) || defined(CONFIG_RISCV)
Expand Down
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