module: Move version support into a separate file

No functional change.

This patch migrates module version support out of core code into
kernel/module/version.c. In addition simple code refactoring to
make this possible.

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

kernel/module/version.c

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Module version support
+ *
+ * Copyright (C) 2008 Rusty Russell
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/printk.h>
+#include "internal.h"
+
+static u32 resolve_rel_crc(const s32 *crc)
+{
+	return *(u32 *)((void *)crc + *crc);
+}
+
+int check_version(const struct load_info *info,
+		  const char *symname,
+			 struct module *mod,
+			 const s32 *crc)
+{
+	Elf_Shdr *sechdrs = info->sechdrs;
+	unsigned int versindex = info->index.vers;
+	unsigned int i, num_versions;
+	struct modversion_info *versions;
+
+	/* Exporting module didn't supply crcs?  OK, we're already tainted. */
+	if (!crc)
+		return 1;
+
+	/* No versions at all?  modprobe --force does this. */
+	if (versindex == 0)
+		return try_to_force_load(mod, symname) == 0;
+
+	versions = (void *)sechdrs[versindex].sh_addr;
+	num_versions = sechdrs[versindex].sh_size
+		/ sizeof(struct modversion_info);
+
+	for (i = 0; i < num_versions; i++) {
+		u32 crcval;
+
+		if (strcmp(versions[i].name, symname) != 0)
+			continue;
+
+		if (IS_ENABLED(CONFIG_MODULE_REL_CRCS))
+			crcval = resolve_rel_crc(crc);
+		else
+			crcval = *crc;
+		if (versions[i].crc == crcval)
+			return 1;
+		pr_debug("Found checksum %X vs module %lX\n",
+			 crcval, versions[i].crc);
+		goto bad_version;
+	}
+
+	/* Broken toolchain. Warn once, then let it go.. */
+	pr_warn_once("%s: no symbol version for %s\n", info->name, symname);
+	return 1;
+
+bad_version:
+	pr_warn("%s: disagrees about version of symbol %s\n", info->name, symname);
+	return 0;
+}
+
+int check_modstruct_version(const struct load_info *info,
+			    struct module *mod)
+{
+	struct find_symbol_arg fsa = {
+		.name	= "module_layout",
+		.gplok	= true,
+	};
+
+	/*
+	 * Since this should be found in kernel (which can't be removed), no
+	 * locking is necessary -- use preempt_disable() to placate lockdep.
+	 */
+	preempt_disable();
+	if (!find_symbol(&fsa)) {
+		preempt_enable();
+		BUG();
+	}
+	preempt_enable();
+	return check_version(info, "module_layout", mod, fsa.crc);
+}
+
+/* First part is kernel version, which we ignore if module has crcs. */
+int same_magic(const char *amagic, const char *bmagic,
+	       bool has_crcs)
+{
+	if (has_crcs) {
+		amagic += strcspn(amagic, " ");
+		bmagic += strcspn(bmagic, " ");
+	}
+	return strcmp(amagic, bmagic) == 0;
+}
+
+/*
+ * Generate the signature for all relevant module structures here.
+ * If these change, we don't want to try to parse the module.
+ */
+void module_layout(struct module *mod,
+		   struct modversion_info *ver,
+		   struct kernel_param *kp,
+		   struct kernel_symbol *ks,
+		   struct tracepoint * const *tp)
+{
+}
+EXPORT_SYMBOL(module_layout);