linux-kernel - Question about pe file verification

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Date:   Mon, 3 Sep 2018 16:31:56 +0800
From:   Xiongwei Song <sxwjean@...il.com>
To:     dhowells@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net
Cc:     keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Question about pe file verification

Hi,

Some code logic I don't understand about the function pefile_digest_pe_contents
 in the file crypto/asymmetric_keys/verify_pefile.c.
At the end of pefile_digest_pe_contents, please see the comment [sxw] below:

static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen,
                     struct pefile_context *ctx,
                     struct shash_desc *desc)
{
    unsigned *canon, tmp, loop, i, hashed_bytes;
    int ret;

    ......
　[sxw] I assume the image has signed by sbsign tool, there is a certificate
             at the end of image file.
    if (pelen > hashed_bytes) {
        tmp = hashed_bytes + ctx->certs_size;
        [sxw] The tmp value is the end of certificate.

        ret = crypto_shash_update(desc,
                      pebuf + hashed_bytes,
                      [sxw] The data address is the beginning of the
certificate.
                               Why do we need to hash the
certification data block?

                      pelen - tmp);
                      [sxw] However, the data length doesn't include
the certificate,
                               sometimes it's zero.

        if (ret < 0)
            return ret;
    }

    return 0;
}

Is that for a special consider or something else?

Regards,
Xiongwei