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"""Validate the IFWI image's OWN internal checksums.
This is independent of how we dumped it: if the image had bitrot, AMD's own
directory checksums would fail. Two independently-obtained dumps agreeing is
suggestive; the image validating its own checksums is much stronger.
"""
import struct, sys, zlib
def fletcher32(data: bytes) -> int:
s1 = s2 = 0xFFFF
for i in range(0, len(data) - 1, 2):
s1 = (s1 + struct.unpack_from('<H', data, i)[0]) % 0xFFFF
s2 = (s2 + s1) % 0xFFFF
return (s2 << 16) | s1
def try_all(name, stored, body):
cands = {
"fletcher32": fletcher32(body),
"crc32": zlib.crc32(body) & 0xFFFFFFFF,
"sum32": sum(struct.unpack_from('<%dI' % (len(body)//4), body, 0)) & 0xFFFFFFFF,
"sumbytes": sum(body) & 0xFFFFFFFF,
}
hit = [k for k, v in cands.items() if v == stored]
print(" %-22s stored=%#010x %s" % (name, stored,
("MATCH via %s" % hit[0]) if hit else "no match (%s)" %
", ".join("%s=%#x" % (k, v) for k, v in cands.items())))
return bool(hit)
def check(path):
img = open(path, 'rb').read()
print("\n=== %s (%d bytes) ===" % (path, len(img)))
ok = True
# --- $PSP directories -------------------------------------------------
for off in (0x2000, 0x3000):
if img[off:off+4] != b'$PSP':
print(" %#07x: no $PSP magic (%s)" % (off, img[off:off+4])); ok = False; continue
stored = struct.unpack_from('<I', img, off+4)[0]
count = struct.unpack_from('<I', img, off+8)[0]
total = 16 + count*16
print(" $PSP @ %#07x entries=%d total=%#x" % (off, count, total))
# AMD fletcher32 runs over everything after the checksum field
if not try_all("dir body (+8..end)", stored, img[off+8:off+total]): ok = False
# --- ISH headers ------------------------------------------------------
for off, name in ((0x12000, "ISH A"), (0x13000, "ISH B")):
w = struct.unpack_from('<8I', img, off)
stored, gen, poff, psize = w[0], w[1], w[4], w[6]
print(" %s @ %#07x gen=%d payload=%#x size=%#x" % (name, off, gen, poff, psize))
if poff + psize <= len(img):
if not try_all("payload", stored, img[poff:poff+psize]): ok = False
else:
print(" payload out of range"); ok = False
return ok
paths = sys.argv[1:] or ["psp_out/flash_KNOWNGOOD_20260917.bin", "psp_out/spiflash.bin"]
for p in paths: check(p)
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