ima: Access decompressed kernel module to verify appended signature

ima: Access decompressed kernel module to verify appended signature

Currently, when in-kernel module decompression (CONFIG_MODULE_DECOMPRESS)
is enabled, IMA has no way to verify the appended module signature as it
can't decompress the module.

Define a new kernel_read_file_id enumerate READING_MODULE_COMPRESSED so
IMA can calculate the compressed kernel module data hash on
READING_MODULE_COMPRESSED and defer appraising/measuring it until on
READING_MODULE when the module has been decompressed.

Before enabling in-kernel module decompression, a kernel module in
initramfs can still be loaded with ima_policy=secure_boot. So adjust the
kernel module rule in secure_boot policy to allow either an IMA
signature OR an appended signature i.e. to use
"appraise func=MODULE_CHECK appraise_type=imasig|modsig".

Reported-by: Karel Srot <ksrot@redhat.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>