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

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Message-ID: <20170530071022.GB26483@linaro.org>
Date:   Tue, 30 May 2017 16:10:23 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     dhowells@...hat.com
Cc:     ard.biesheuvel@...aro.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: verify_pefile_signature() and a message field of MZ header in pe.h

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