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Harden vector bootloaders more against reset overwrites

This commit is contained in:
Stefan Rueger 2022-11-09 19:28:29 +00:00
parent 84a3e2cc2b
commit d5d0b940cc
No known key found for this signature in database
GPG Key ID: B0B4F1FD86B1EC55
1 changed files with 41 additions and 32 deletions
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49
src/urclock.c
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@ -637,7 +637,7 @@ static int urclock_flash_readhook(const PROGRAMMER *pgm, const AVRPART *p, const
}
if(llcode && !llvectors && ur.vblvectornum > 0 && ur.vbllevel)
pmsg_warning("not patching input as it appears to not start with a vector table\n");
pmsg_warning("not patching jmp to application as input does not start with a vector table\n");
// Patch vectors if input looks like code and it's a vector bootloader with known vector number
if(llcode && llvectors && ur.vblvectornum > 0 && ur.vbllevel) {
@ -807,19 +807,14 @@ nopatch_nometa:
// Last, but not least: ensure that vector bootloaders have correct r/jmp at address 0
if(ur.blstart && ur.vbllevel==1) {
int set=0;
int rc, set=0;
for(int i=0; i < vecsz; i++)
if(flm->tags[i] & TAG_ALLOCATED)
set++;
// Reset vector not programmed and flash readable: check what's on the flash
if(set != vecsz && (!ur.urprotocol || (ur.urfeatures & UB_READ_FLASH))) {
unsigned char device[2048], jmptoboot[4];
int rc;
// Read reset vector on device flash
if((rc = ur_readEF(pgm, p, device, 0, vecsz, 'F')) < 0)
return rc;
// Reset vector not programmed? Or -F? Ensure a jmp to bootloader
if(ovsigck || set != vecsz) {
unsigned char jmptoboot[4];
// What reset *should* look like
if(vecsz == 4)
@ -827,8 +822,15 @@ nopatch_nometa:
else
uint16tobuf(jmptoboot, rjmp_opcode(ur.blstart - 0, ur.uP.flashsize));
if(!ur.urprotocol || (ur.urfeatures & UB_READ_FLASH)) { // Flash readable?
unsigned char device[2048];
// Read reset vector from device flash
if((rc = ur_readEF(pgm, p, device, 0, vecsz, 'F')) < 0)
return rc;
int changed = 0;
for(int i=0; i < vecsz; i++) { // Patch reset vector to protect vector bootloader
for(int i=0; i < vecsz; i++) {
if((flm->tags[i] & TAG_ALLOCATED? flm->buf[i]: device[i]) != jmptoboot[i]) {
flm->buf[i] = jmptoboot[i];
flm->tags[i] |= TAG_ALLOCATED;
@ -837,6 +839,7 @@ nopatch_nometa:
}
// If reset vector patched, ensure to fill in the holes in rest of page
if(changed && flm->page_size > vecsz && flm->page_size <= sizeof device) {
pmsg_warning("patching reset vector to protect vector bootloader\n");
if((rc = ur_readEF(pgm, p, device+vecsz, vecsz, flm->page_size - vecsz, 'F')) < 0)
return rc;
for(int i=vecsz; i < flm->page_size; i++) {
@ -846,15 +849,19 @@ nopatch_nometa:
}
}
}
} else if(set && set != vecsz)
Return("input overwrites reset vector, which would render the vector bootloader inoperable");
if(set) {
} else { // Flash not readable: patch reset vector
for(int i=0; i < vecsz; i++) {
flm->buf[i] = jmptoboot[i];
flm->tags[i] |= TAG_ALLOCATED;
}
}
} else { // Double-check reset vector jumps to bootloader
int resetdest;
if(reset2addr(flm->buf, vecsz, flm->size, &resetdest) < 0)
Return("input would overwrite the reset vector making the vector bootloader unreachable");
Return("input overwrites the reset vector bricking the bootloader; use -F to patch input");
if(resetdest != ur.blstart)
Return("input file points reset to 0x%04x instead of vector bootloader at 0x%04x, exiting",
Return("input points reset to 0x%04x, not to bootloader at 0x%04x; use -F to patch input",
resetdest, ur.blstart);
}
}
@ -891,7 +898,7 @@ static void urbootPutVersion(char *buf, uint16_t ver) {
*buf++ = type & UR_RESETFLAGS? 'r': '-';
*buf = 0;
} else if(hi) // Version number in binary from optiboot v4.1
sprintf(buf, "o%d.%d ??s-??%c", hi, type, hi>=4? 'r': '-');
sprintf(buf, "o%d.%d -?s-?-%c", hi, type, hi>=4? 'r': '-');
else
sprintf(buf, "x0.0 -------");
@ -1931,7 +1938,8 @@ static int urclock_paged_write(const PROGRAMMER *pgm, const AVRPART *p, const AV
return -2;
if(mchr == 'E' && !ur.bleepromrw && !ur.xeepromrw)
Return("bootloader does not %shave paged EEPROM write capability", ur.blurversion? "": "seem to ");
Return("bootloader does not %shave paged EEPROM write capability",
ur.blurversion? "": "seem to ");
n = addr + n_bytes;
@ -1965,7 +1973,8 @@ static int urclock_paged_load(const PROGRAMMER *pgm, const AVRPART *p, const AVR
Return("bootloader does not have flash read capability");
if(mchr == 'E' && !ur.bleepromrw && !ur.xeepromrw)
Return("bootloader does not %shave paged EEPROM read capability", ur.blurversion? "": "seem to ");
Return("bootloader does not %shave paged EEPROM read capability",
ur.blurversion? "": "seem to ");
n = addr + n_bytes;
for(; addr < n; addr += chunk) {