Module verification already implements appeded signature check.

Reuse it for kexec_file.

The kexec_file implementation uses EKEYREJECTED error in some cases when
there is no key and the common implementation uses ENOPKG or EBADMSG
instead.

Signed-off-by: Michal Suchanek <msucha...@suse.de>
Acked-by: Heiko Carstens <h...@linux.ibm.com>
---
v3: Philipp Rudo <pr...@redhat.com>: Update the commit with note about
change of return value
---
 arch/s390/kernel/machine_kexec_file.c | 22 +++++-----------------
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/arch/s390/kernel/machine_kexec_file.c 
b/arch/s390/kernel/machine_kexec_file.c
index 8f43575a4dd3..c944d71316c7 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -31,6 +31,7 @@ int s390_verify_sig(const char *kernel, unsigned long 
kernel_len)
        const unsigned long marker_len = sizeof(MODULE_SIG_STRING) - 1;
        struct module_signature *ms;
        unsigned long sig_len;
+       int ret;
 
        /* Skip signature verification when not secure IPLed. */
        if (!ipl_secure_flag)
@@ -45,25 +46,12 @@ int s390_verify_sig(const char *kernel, unsigned long 
kernel_len)
        kernel_len -= marker_len;
 
        ms = (void *)kernel + kernel_len - sizeof(*ms);
-       kernel_len -= sizeof(*ms);
+       ret = mod_check_sig(ms, kernel_len, "kexec");
+       if (ret)
+               return ret;
 
        sig_len = be32_to_cpu(ms->sig_len);
-       if (sig_len >= kernel_len)
-               return -EKEYREJECTED;
-       kernel_len -= sig_len;
-
-       if (ms->id_type != PKEY_ID_PKCS7)
-               return -EKEYREJECTED;
-
-       if (ms->algo != 0 ||
-           ms->hash != 0 ||
-           ms->signer_len != 0 ||
-           ms->key_id_len != 0 ||
-           ms->__pad[0] != 0 ||
-           ms->__pad[1] != 0 ||
-           ms->__pad[2] != 0) {
-               return -EBADMSG;
-       }
+       kernel_len -= sizeof(*ms) + sig_len;
 
        return verify_pkcs7_signature(kernel, kernel_len,
                                      kernel + kernel_len, sig_len,
-- 
2.31.1

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