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embed/trezorhal: introduce jump_to_unprivileged, disable mpu in bootloader

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Pavol Rusnak 2018-02-13 20:50:40 +01:00
parent 302a31e8d2
commit 5ded086800
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GPG Key ID: 91F3B339B9A02A3D
4 changed files with 59 additions and 5 deletions
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4
embed/bootloader/main.c
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@ -354,7 +354,9 @@ main_start:
ui_fadeout();
}
mpu_config();
// mpu_config();
// jump_to_unprivileged(FIRMWARE_START + vhdr.hdrlen + IMAGE_HEADER_SIZE);
jump_to(FIRMWARE_START + vhdr.hdrlen + IMAGE_HEADER_SIZE);
return 0;

4
embed/bootloader/mpu.c
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@ -53,8 +53,4 @@ void mpu_config(void)
// Enable MPU
HAL_MPU_Enable(0);
// Switch to unprivileged mode
// http://infocenter.arm.com/help/topic/com.arm.doc.dui0552a/CHDBIBGJ.html
__asm__ volatile("msr control, %0" :: "r" (0x1));
}

1
embed/trezorhal/common.h
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@ -18,5 +18,6 @@ extern uint32_t __stack_chk_guard;
void memset_reg(volatile void *start, volatile void *stop, uint32_t val);
void jump_to(uint32_t address);
void jump_to_unprivileged(uint32_t address);
#endif

55
embed/trezorhal/util.s
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@ -66,6 +66,61 @@ jump_to:
ldr lr, [lr, 4] // set lr to the next stage's reset_handler
bx lr
.global jump_to_unprivileged
.type jump_to_unprivileged, STT_FUNC
jump_to_unprivileged:
mov r4, r0 // save input argument r0 (the address of the next stage's vector table) (r4 is callee save)
// this subroutine re-points the exception handlers before the C code
// that comprises them has been given a good environment to run.
// therefore, this code needs to disable interrupts before the VTOR
// update. then, the reset_handler of the next stage needs to re-enable interrupts.
// the following prevents activation of all exceptions except Non-Maskable Interrupt (NMI).
// according to "ARM Cortex-M Programming Guide to Memory Barrier Instructions" Application Note 321, section 4.8:
// "there is no requirement to insert memory barrier instructions after CPSID".
cpsid f
// wipe memory at the end of the current stage of code
bl clear_otg_hs_memory
ldr r0, =ccmram_start // r0 - point to beginning of CCMRAM
ldr r1, =ccmram_end // r1 - point to byte after the end of CCMRAM
ldr r2, =0 // r2 - the word-sized value to be written
bl memset_reg
ldr r0, =sram_start // r0 - point to beginning of SRAM
ldr r1, =sram_end // r1 - point to byte after the end of SRAM
ldr r2, =0 // r2 - the word-sized value to be written
bl memset_reg
mov lr, r4
// clear out the general purpose registers before the next stage's code can run (even the NMI exception handler)
ldr r0, =0
mov r1, r0
mov r2, r0
mov r3, r0
mov r4, r0
mov r5, r0
mov r6, r0
mov r7, r0
mov r8, r0
mov r9, r0
mov r10, r0
mov r11, r0
mov r12, r0
// give the next stage a fresh main stack pointer
ldr r0, [lr] // set r0 to the main stack pointer in the next stage's vector table
msr msp, r0 // give the next stage its main stack pointer
// point to the next stage's exception handlers
// AN321, section 4.11: "a memory barrier is not required after a VTOR update"
.set SCB_VTOR, 0xE000ED08 // reference "Cortex-M4 Devices Generic User Guide" section 4.3
ldr r0, =SCB_VTOR
str lr, [r0]
mov r0, r1 // zero out r0
// go on to the next stage
ldr lr, [lr, 4] // set lr to the next stage's reset_handler
// switch to unprivileged mode
ldr r0, =1
msr control, r0
isb
// jump
bx lr
.global shutdown
.type shutdown, STT_FUNC
shutdown: