kexec: replace call to copy_file_from_fd() with kernel version

Replace copy_file_from_fd() with kernel_read_file_from_fd().

Two new identifiers named READING_KEXEC_IMAGE and READING_KEXEC_INITRAMFS
are defined for measuring, appraising or auditing the kexec image and
initramfs.

Changelog v3:
- return -EBADF, not -ENOEXEC
- identifier change
- split patch, moving copy_file_from_fd() to a separate patch
- split patch, moving IMA changes to a separate patch
v0:
- use kstat file size type loff_t, not size_t
- Calculate the file hash from the in memory buffer - Dave Young

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Acked-by: Dave Young <dyoung@redhat.com>

include/linux/fs.h

@@ -2579,6 +2579,8 @@ extern int do_pipe_flags(int *, int);
 enum kernel_read_file_id {
 	READING_FIRMWARE = 1,
 	READING_MODULE,
+	READING_KEXEC_IMAGE,
+	READING_KEXEC_INITRAMFS,
 	READING_MAX_ID
 };