[PATCH 3/3] module: Improve module __ro_after_init handling

From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Jessica Yu <jeyu@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Petr Mladek <pmladek@suse.com>, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
	Johannes Erdfelt <johannes@erdfelt.com>,
	Ingo Molnar <mingo@kernel.org>
Subject: [PATCH 3/3] module: Improve module __ro_after_init handling
Date: Thu, 13 Jun 2019 20:07:24 -0500	[thread overview]
Message-ID: <1b72f40d863a1444f687b3e1b958bdc6925882ed.1560474114.git.jpoimboe@redhat.com> (raw)
In-Reply-To: <cover.1560474114.git.jpoimboe@redhat.com>

module_enable_ro() can be called in the following scenario:

  [load livepatch module]
    initcall
      klp_enable_patch()
        klp_init_patch()
          klp_init_object()
            klp_init_object_loaded()
              module_enable_ro(pmod, true)

In this case, module_enable_ro()'s 'after_init' argument is true, which
prematurely changes the module's __ro_after_init area to read-only.

If, theoretically, a registrant of the MODULE_STATE_LIVE module notifier
tried to write to the livepatch module's __ro_after_init section, an
oops would occur.

Remove the 'after_init' argument and instead make __module_enable_ro()
smart enough to only frob the __ro_after_init section after the module
has gone live.

Reported-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/arm64/kernel/ftrace.c |  2 +-
 include/linux/module.h     |  4 ++--
 kernel/livepatch/core.c    |  4 ++--
 kernel/module.c            | 14 +++++++-------
 4 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 65a51331088e..c17d98aafc93 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -120,7 +120,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 			/* point the trampoline to our ftrace entry point */
 			module_disable_ro(mod);
 			*mod->arch.ftrace_trampoline = trampoline;
-			module_enable_ro(mod, true);
+			module_enable_ro(mod);
 
 			/* update trampoline before patching in the branch */
 			smp_wmb();
diff --git a/include/linux/module.h b/include/linux/module.h
index 188998d3dca9..4d6922f3760e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -844,12 +844,12 @@ extern int module_sysfs_initialized;
 #ifdef CONFIG_STRICT_MODULE_RWX
 extern void set_all_modules_text_rw(void);
 extern void set_all_modules_text_ro(void);
-extern void module_enable_ro(const struct module *mod, bool after_init);
+extern void module_enable_ro(const struct module *mod);
 extern void module_disable_ro(const struct module *mod);
 #else
 static inline void set_all_modules_text_rw(void) { }
 static inline void set_all_modules_text_ro(void) { }
-static inline void module_enable_ro(const struct module *mod, bool after_init) { }
+static inline void module_enable_ro(const struct module *mod) { }
 static inline void module_disable_ro(const struct module *mod) { }
 #endif
 
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index c4ce08f43bd6..f9882ffa2f44 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -724,13 +724,13 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	module_disable_ro(patch->mod);
 	ret = klp_write_object_relocations(patch->mod, obj);
 	if (ret) {
-		module_enable_ro(patch->mod, true);
+		module_enable_ro(patch->mod);
 		mutex_unlock(&text_mutex);
 		return ret;
 	}
 
 	arch_klp_init_object_loaded(patch, obj);
-	module_enable_ro(patch->mod, true);
+	module_enable_ro(patch->mod);
 
 	mutex_unlock(&text_mutex);
 
diff --git a/kernel/module.c b/kernel/module.c
index e43a90ee2d23..fb3561e0c5b0 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1956,7 +1956,7 @@ void module_disable_ro(const struct module *mod)
 	frob_rodata(&mod->init_layout, set_memory_rw);
 }
 
-void __module_enable_ro(const struct module *mod, bool after_init)
+static void __module_enable_ro(const struct module *mod)
 {
 	if (!rodata_enabled)
 		return;
@@ -1973,15 +1973,15 @@ void __module_enable_ro(const struct module *mod, bool after_init)
 
 	frob_rodata(&mod->init_layout, set_memory_ro);
 
-	if (after_init)
+	if (mod->state == MODULE_STATE_LIVE)
 		frob_ro_after_init(&mod->core_layout, set_memory_ro);
 }
 
-void module_enable_ro(const struct module *mod, bool after_init)
+void module_enable_ro(const struct module *mod)
 {
 	lockdep_assert_held(&text_mutex);
 
-	__module_enable_ro(mod, after_init);
+	__module_enable_ro(mod);
 }
 
 static void __module_enable_nx(const struct module *mod)
@@ -2041,7 +2041,7 @@ void set_all_modules_text_ro(void)
 	mutex_unlock(&module_mutex);
 }
 #else
-static void __module_enable_ro(const struct module *mod, bool after_init) { }
+static void __module_enable_ro(const struct module *mod) { }
 static void __module_enable_nx(const struct module *mod) { }
 #endif
 
@@ -3534,7 +3534,7 @@ static noinline int do_init_module(struct module *mod)
 	/* Switch to core kallsyms now init is done: kallsyms may be walking! */
 	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
 #endif
-	__module_enable_ro(mod, true);
+	__module_enable_ro(mod);
 	mod_tree_remove_init(mod);
 	module_arch_freeing_init(mod);
 	mod->init_layout.base = NULL;
@@ -3641,7 +3641,7 @@ 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);
 
-	__module_enable_ro(mod, false);
+	__module_enable_ro(mod);
 	__module_enable_nx(mod);
 
 	/* Mark state as coming so strong_try_module_get() ignores us,
-- 
2.20.1

