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firmware: add crc stub to all dfu apps to ensure reliable loading

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DFU flashing of apps sometimes aborts, and although rare this leads to
broken devices if no boot button or serial/jtag access exists, because
the bootloader will keep trying to start a half-flashed app that then
crashes at some point.

The easiest fix that works with existing bootloaders is to prepend a
small 512 byte stub that calculcates the crc and compares it with the
crc calculated at build time, and then either starts the actual app, or
sets the dfu flag and resets. This ensures we either have a working,
running app, or end up in the bootloader, ready to flash again.

For obvious reasons this only applies to dfu apps, and not to flash
targets like the actual bootloader itself.

Change-Id: Id6df0486c8b779889d21800dc2441b3aa9af8a5f
This commit is contained in:
Eric Wild
2021-12-06 21:48:01 +01:00
committed by laforge
parent f721e69bc1
commit cb655f9774
7 changed files with 246 additions and 28 deletions
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86
firmware/libcommon/source/crcstub.c Normal file
View File

@@ -0,0 +1,86 @@
/* SIMtrace 2 firmware crc stub
*
* (C) 2021 by sysmocom -s.f.m.c. GmbH, Author: Eric Wild <ewild@sysmocom.de>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <stdint.h>
#include "board.h"
#include "core_cm3.h"
#include "usb/device/dfu/dfu.h"
/*
* This file is a bit special, everything has to go to specific sections, and no globals are available.
* No external functions may be called, unless inlining is enforced!
*/
static void crc_check_stub();
__attribute__((section(".crcstub_table"))) volatile uint32_t crcstub_dummy_table[] = {
(uint32_t)0xdeadc0de, /* deliberately choose invalid value so unpatched image will not be started */
(uint32_t)crc_check_stub, /* must be valid flash addr */
(uint32_t)0xf1, /* crc value calculated by the host */
(uint32_t)0xf2, /* crc calc start address */
(uint32_t)0xf3 /* crc calc length (byte) */
};
__attribute__((section(".crcstub_code"))) static void do_crc32(int8_t c, uint32_t *crc_reg)
{
int32_t i, mask;
*crc_reg ^= c;
for (unsigned int j = 0; j < 8; j++)
if (*crc_reg & 1)
*crc_reg = (*crc_reg >> 1) ^ 0xEDB88320;
else
*crc_reg = *crc_reg >> 1;
}
__attribute__((section(".crcstub_code"), noinline)) static void crc_check_stub()
{
uint32_t crc_reg = 0xffffffff;
uint32_t expected_crc_val = crcstub_dummy_table[2];
uint8_t *crc_calc_startaddr = (uint8_t *)crcstub_dummy_table[3];
volatile uint32_t *actual_exc_tbl = (volatile uint32_t *)crc_calc_startaddr;
uint32_t crc_len = crcstub_dummy_table[4];
/* 4000ms wdt tickling */
WDT->WDT_MR = WDT_MR_WDRSTEN | WDT_MR_WDDBGHLT | WDT_MR_WDIDLEHLT | (((4000UL << 8) / 1000) << 16) |
((4000UL << 8) / 1000);
for (uint8_t *i = crc_calc_startaddr; i < crc_calc_startaddr + crc_len; i++)
do_crc32(*i, &crc_reg);
crc_reg = ~crc_reg;
if (crc_reg == expected_crc_val) {
/* this looks a bit awkward because we have to ensure the bx does not require a sp-relative load */
__asm__ volatile("\
mov r0, %0;\n\
mov r1, %1;\n\
MSR msp,r0;\n\
bx r1;"
:
: "r"(actual_exc_tbl[0]), "r"(actual_exc_tbl[1]));
} else {
/* no globals ! */
((struct dfudata *)0x20000000)->magic = USB_DFU_MAGIC;
__DSB();
for (;;) {
/* no functon call, since NVIC_SystemReset() might not be inlined! */
SCB->AIRCR = ((0x5FA << SCB_AIRCR_VECTKEY_Pos) | (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
SCB_AIRCR_SYSRESETREQ_Msk);
__DSB();
while (1)
;
}
}
}