kbuild: align modinfo section for Secureboot Authenticode EDK2 compat

Previously linker scripts would always generate vmlinuz that has sections
aligned. And thus padded (correct Authenticode calculation) and unpadded
calculation would be same. As in https://github.com/rhboot/pesign userspace
tool would produce the same authenticode digest for both of the following
commands:

    pesign --padding --hash --in ./arch/x86_64/boot/bzImage
    pesign --nopadding --hash --in ./arch/x86_64/boot/bzImage

The commit 3e86e4d ("kbuild: keep .modinfo section in
vmlinux.unstripped") added .modinfo section of variable length. Depending
on kernel configuration it may or may not be aligned.

All userspace signing tooling correctly pads such section to calculation
spec compliant authenticode digest.

However, if bzImage is not further processed and is attempted to be loaded
directly by EDK2 firmware, it calculates unpadded Authenticode digest and
fails to correct accept/reject such kernel builds even when propoer
Authenticode values are enrolled in db/dbx. One can say EDK2 requires
aligned/padded kernels in Secureboot.

Thus add ALIGN(8) to the .modinfo section, to esure kernels irrespective of
modinfo contents can be loaded by all existing EDK2 firmware builds.

Fixes: 3e86e4d ("kbuild: keep .modinfo section in vmlinux.unstripped")
Cc: stable@vger.kernel.org
Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@surgut.co.uk>
Link: https://patch.msgid.link/20251026202100.679989-1-dimitri.ledkov@surgut.co.uk
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: xnox

include/asm-generic/vmlinux.lds.h

@@ -832,7 +832,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 
 /* Required sections not related to debugging. */
 #define ELF_DETAILS							\
-		.modinfo : { *(.modinfo) }				\
+		.modinfo : { *(.modinfo) . = ALIGN(8); }		\
 		.comment 0 : { *(.comment) }				\
 		.symtab 0 : { *(.symtab) }				\
 		.strtab 0 : { *(.strtab) }				\