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

From: Josh Poimboeuf
Date: Thu Jun 13 2019 - 21:13:32 EST


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@xxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
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