module: Rework layout alignment to avoid BUG_ON()s

Perform layout alignment verification up front and WARN_ON()
and fail module loading instead of crashing the machine.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Author: chleroy

kernel/module/internal.h

@@ -180,6 +180,7 @@ void module_enable_nx(const struct module *mod);
 void module_enable_x(const struct module *mod);
 int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 				char *secstrings, struct module *mod);
+bool module_check_misalignment(const struct module *mod);
 
 #ifdef CONFIG_MODULE_SIG
 int module_sig_check(struct load_info *info, int flags);

kernel/module/main.c

@@ -2550,6 +2550,9 @@ static int complete_formation(struct module *mod, struct load_info *info)
 	/* This relies on module_mutex for list integrity. */
 	module_bug_finalize(info->hdr, info->sechdrs, mod);
 
+	if (module_check_misalignment(mod))
+		goto out_misaligned;
+
 	module_enable_ro(mod, false);
 	module_enable_nx(mod);
 	module_enable_x(mod);
@@ -2563,6 +2566,8 @@ static int complete_formation(struct module *mod, struct load_info *info)
 
 	return 0;
 
+out_misaligned:
+	err = -EINVAL;
 out:
 	mutex_unlock(&module_mutex);
 	return err;

kernel/module/strict_rwx.c

@@ -42,33 +42,42 @@ static void frob_text(const struct module_layout *layout,
 static void frob_rodata(const struct module_layout *layout,
 		 int (*set_memory)(unsigned long start, int num_pages))
 {
-	BUG_ON(!PAGE_ALIGNED(layout->base));
-	BUG_ON(!PAGE_ALIGNED(layout->text_size));
-	BUG_ON(!PAGE_ALIGNED(layout->ro_size));
 	set_memory((unsigned long)layout->base + layout->text_size,
 		   (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
 }
 
 static void frob_ro_after_init(const struct module_layout *layout,
 			int (*set_memory)(unsigned long start, int num_pages))
 {
-	BUG_ON(!PAGE_ALIGNED(layout->base));
-	BUG_ON(!PAGE_ALIGNED(layout->ro_size));
-	BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
 	set_memory((unsigned long)layout->base + layout->ro_size,
 		   (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
 }
 
 static void frob_writable_data(const struct module_layout *layout,
 			int (*set_memory)(unsigned long start, int num_pages))
 {
-	BUG_ON(!PAGE_ALIGNED(layout->base));
-	BUG_ON(!PAGE_ALIGNED(layout->ro_after_init_size));
-	BUG_ON(!PAGE_ALIGNED(layout->size));
 	set_memory((unsigned long)layout->base + layout->ro_after_init_size,
 		   (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
 }
 
+static bool layout_check_misalignment(const struct module_layout *layout)
+{
+	return WARN_ON(!PAGE_ALIGNED(layout->base)) ||
+	       WARN_ON(!PAGE_ALIGNED(layout->text_size)) ||
+	       WARN_ON(!PAGE_ALIGNED(layout->ro_size)) ||
+	       WARN_ON(!PAGE_ALIGNED(layout->ro_after_init_size)) ||
+	       WARN_ON(!PAGE_ALIGNED(layout->size));
+}
+
+bool module_check_misalignment(const struct module *mod)
+{
+	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+		return false;
+
+	return layout_check_misalignment(&mod->core_layout) ||
+	       layout_check_misalignment(&mod->init_layout);
+}
+
 void module_enable_x(const struct module *mod)
 {
 	if (!PAGE_ALIGNED(mod->core_layout.base) ||