linux-kernel - [RFC PATCH 3/3] module: pre-test setting ro_after

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Message-ID: <a32f2390caf6e0d157ffea6e04f5e5d8629620c2.1731148254.git.christophe.leroy@csgroup.eu>
Date: Sat,  9 Nov 2024 11:35:37 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	Kees Cook <kees@...nel.org>,
	linux-modules@...r.kernel.org
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC PATCH 3/3] module: pre-test setting ro_after_init data read-only

To be on the safe side, try to set ro_after_init data section readonly
at the same time as rodata. If it fails it will likely fail again
later so let's cancel module loading while we still can do it.
If it doesn't fail, put it back to read-only, continue module loading
and cross fingers so that it still works after module init. Then it
should in principle never fail so add a WARN_ON_ONCE() to get a big
fat warning in case it happens anyway.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 kernel/module/main.c       | 2 +-
 kernel/module/strict_rwx.c | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 1bf4b0db291b..b603c9647e73 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2582,7 +2582,7 @@ static noinline int do_init_module(struct module *mod)
 	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
 #endif
 	ret = module_enable_rodata_ro_after_init(mod);
-	if (ret)
+	if (WARN_ON_ONCE(ret))
 		pr_warn("%s: %s() returned %d, ro_after_init data might still be writable\n",
 			mod->name, __func__, ret);
 
diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
index f68c59974ae2..329afd43f06b 100644
--- a/kernel/module/strict_rwx.c
+++ b/kernel/module/strict_rwx.c
@@ -58,7 +58,10 @@ int module_enable_rodata_ro(const struct module *mod)
 	if (ret)
 		return ret;
 
-	return 0;
+	ret = module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_ro);
+	if (ret)
+		return ret;
+	return module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_rw);
 }
 
 int module_enable_rodata_ro_after_init(const struct module *mod)
-- 
2.44.0