module: add module_elf_check_arch for module-specific checks

The elf_check_arch() function is also used to test compatibility of
usermode binaries. Kernel modules may have more specific requirements,
for example powerpc would like to test for ABI version compatibility.

Add a weak module_elf_check_arch() that defaults to true, and call it
from elf_validity_check().
Signed-off-by: Jessica Yu <jeyu@kernel.org>
[np: added changelog, adjust name, rebase]
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221128041539.1742489-2-npiggin@gmail.com

include/linux/moduleloader.h

@@ -13,6 +13,9 @@
  * must be implemented by each architecture.
  */
 
+/* arch may override to do additional checking of ELF header architecture */
+bool module_elf_check_arch(Elf_Ehdr *hdr);
+
 /* Adjust arch-specific sections.  Return 0 on success.  */
 int module_frob_arch_sections(Elf_Ehdr *hdr,
 			      Elf_Shdr *sechdrs,

kernel/module/main.c

@@ -1674,6 +1674,11 @@ static int elf_validity_check(struct load_info *info)
 		       info->hdr->e_machine);
 		goto no_exec;
 	}
+	if (!module_elf_check_arch(info->hdr)) {
+		pr_err("Invalid module architecture in ELF header: %u\n",
+		       info->hdr->e_machine);
+		goto no_exec;
+	}
 	if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
 		pr_err("Invalid ELF section header size\n");
 		goto no_exec;
@@ -2247,6 +2252,11 @@ static void flush_module_icache(const struct module *mod)
 			   (unsigned long)mod->core_layout.base + mod->core_layout.size);
 }
 
+bool __weak module_elf_check_arch(Elf_Ehdr *hdr)
+{
+	return true;
+}
+
 int __weak module_frob_arch_sections(Elf_Ehdr *hdr,
 				     Elf_Shdr *sechdrs,
 				     char *secstrings,