verify_pefile_signature() and a message field of MZ header in pe.h

From: AKASHI Takahiro
Date: Tue May 30 2017 - 03:06:00 EST


Hi David,

Struct mz_hdr in include/linux/pe.h contains a message[] field.
Should it be part of this structure?
(I googled "MZ format," but didn't find out the exact definition.)

I'm now working on kexec_file_load support on arm64. As arm64's
Image binary can be seen as in PE format, verify_pefile_signature()
is used to assure integrity as on x86.
But this attempt fails (ELIBBAD) at pefile_parse_binary():

---8<---
#define chkaddr(base, x, s) \
do { \
if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
return -ELIBBAD; \
} while (0)

...

cursor = sizeof(*mz);

chkaddr(cursor, mz->peaddr, sizeof(*pe)); <-- Here
pe = pebuf + mz->peaddr;
if (pe->magic != PE_MAGIC)
return -ELIBBAD;
--->8---

because our Image doesn't have message[] in a pseudo header and so
mz->peaddr is not beyond sizeof(*mz).

I think we can fix this issue, either
(a) remove message[] from struct mz_hdr
(b) modify a check by chkaddr() macro
(c) add a dummy pad into arm64's binary

Which one should we follow here?

Thanks,
-Takahiro AKASHI