kbuild/modules: Check module symbol versions on insmod

Yeah, the final step!
  
Now that we've got the checksums for the exported symbols and the
checksums of the unresolved symbols for the module we're loading,
let's compare and see.
  
Again, we allow to load a module which has the version info stripped,
but taint the kernel in that case.

kernel/module.c

@@ -725,11 +725,66 @@ static int obsolete_params(const char *name,
 }
 #endif /* CONFIG_OBSOLETE_MODPARM */
 
+#ifdef CONFIG_MODVERSIONING
+static int check_version(Elf_Shdr *sechdrs,
+			 unsigned int versindex,
+			 const char *symname,
+			 struct module *mod, 
+			 struct kernel_symbol_group *ksg,
+			 unsigned int symidx)
+{
+	unsigned long crc;
+	unsigned int i, num_versions;
+	struct modversion_info *versions;
+
+	if (!ksg->crcs) { 
+		printk("%s: no CRC for \"%s\" [%s] found: kernel tainted.\n",
+		       mod->name, symname, 
+		       ksg->owner ? ksg->owner->name : "kernel");
+		goto taint;
+	}
+
+	crc = ksg->crcs[symidx];
+
+	versions = (void *) sechdrs[versindex].sh_addr;
+	num_versions = sechdrs[versindex].sh_size
+		/ sizeof(struct modversion_info);
+
+	for (i = 0; i < num_versions; i++) {
+		if (strcmp(versions[i].name, symname) != 0)
+			continue;
+
+		if (versions[i].crc == crc)
+			return 1;
+		printk("%s: disagrees about version of symbol %s\n",
+		       mod->name, symname);
+		DEBUGP("Found checksum %lX vs module %lX\n",
+		       crc, versions[i].crc);
+		return 0;
+	}
+	/* Not in module's version table.  OK, but that taints the kernel. */
+	printk("%s: no version for \"%s\" found: kernel tainted.\n",
+	       mod->name, symname);
+ taint:
+	tainted |= TAINT_FORCED_MODULE;
+	return 1;
+}
+#else
+static inline int check_version(Elf_Shdr *sechdrs,
+				unsigned int versindex,
+				const char *symname,
+				struct module *mod, 
+				struct kernel_symbol_group *ksg,
+				unsigned int symidx)
+{
+	return 1;
+}
+#endif /* CONFIG_MODVERSIONING */
+
 /* Resolve a symbol for this module.  I.e. if we find one, record usage.
    Must be holding module_mutex. */
 static unsigned long resolve_symbol(Elf_Shdr *sechdrs,
-				    unsigned int symindex,
-				    const char *strtab,
+				    unsigned int versindex,
 				    const char *name,
 				    struct module *mod)
 {
@@ -740,8 +795,10 @@ static unsigned long resolve_symbol(Elf_Shdr *sechdrs,
 	spin_lock_irq(&modlist_lock);
 	ret = __find_symbol(name, &ksg, &symidx, mod->license_gplok);
 	if (ret) {
-		/* This can fail due to OOM, or module unloading */
-		if (!use_module(mod, ksg->owner))
+		/* use_module can fail due to OOM, or module unloading */
+		if (!check_version(sechdrs, versindex, name, mod,
+				   ksg, symidx) ||
+		    !use_module(mod, ksg->owner))
 			ret = 0;
 	}
 	spin_unlock_irq(&modlist_lock);
@@ -828,6 +885,7 @@ static int handle_section(const char *name,
 static int simplify_symbols(Elf_Shdr *sechdrs,
 			    unsigned int symindex,
 			    unsigned int strindex,
+			    unsigned int versindex,
 			    struct module *mod)
 {
 	Elf_Sym *sym = (void *)sechdrs[symindex].sh_addr;
@@ -852,7 +910,7 @@ static int simplify_symbols(Elf_Shdr *sechdrs,
 
 		case SHN_UNDEF:
 			sym[i].st_value
-			  = resolve_symbol(sechdrs, symindex, strtab,
+			  = resolve_symbol(sechdrs, versindex,
 					   strtab + sym[i].st_name, mod);
 
 			/* Ok if resolved.  */
@@ -981,7 +1039,7 @@ static struct module *load_module(void *umod,
 	char *secstrings, *args;
 	unsigned int i, symindex, exportindex, strindex, setupindex, exindex,
 		modindex, obsparmindex, licenseindex, gplindex, vmagindex,
-		crcindex, gplcrcindex;
+		crcindex, gplcrcindex, versindex;
 	long arglen;
 	struct module *mod;
 	long err = 0;
@@ -1018,7 +1076,7 @@ static struct module *load_module(void *umod,
 	/* May not export symbols, or have setup params, so these may
            not exist */
 	exportindex = setupindex = obsparmindex = gplindex = licenseindex 
-		= crcindex = gplcrcindex = 0;
+		= crcindex = gplcrcindex = versindex = 0;
 
 	/* And these should exist, but gcc whinges if we don't init them */
 	symindex = strindex = exindex = modindex = vmagindex = 0;
@@ -1089,6 +1147,13 @@ static struct module *load_module(void *umod,
 			DEBUGP("Version magic found in section %u\n", i);
 			vmagindex = i;
 			sechdrs[i].sh_flags &= ~(unsigned long)SHF_ALLOC;
+		} else if (strcmp(secstrings+sechdrs[i].sh_name,
+				  "__versions") == 0 &&
+			   (sechdrs[i].sh_flags & SHF_ALLOC)) {
+			/* Module version info (both exported and needed) */
+			DEBUGP("Versions found in section %u\n", i);
+			versindex = i;
+			sechdrs[i].sh_flags &= ~(unsigned long)SHF_ALLOC;
 		}
 #ifdef CONFIG_KALLSYMS
 		/* symbol and string tables for decoding later. */
@@ -1200,7 +1265,7 @@ static struct module *load_module(void *umod,
 	set_license(mod, sechdrs, licenseindex);
 
 	/* Fix up syms, so that st_value is a pointer to location. */
-	err = simplify_symbols(sechdrs, symindex, strindex, mod);
+	err = simplify_symbols(sechdrs, symindex, strindex, versindex, mod);
 	if (err < 0)
 		goto cleanup;