linux-kernel - [PATCH 2/2] module: Make srcu_struct ptr array as read-only post init

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Message-Id: <20190410011418.76408-2-joel@joelfernandes.org>
Date:   Tue,  9 Apr 2019 21:14:18 -0400
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        paulmck@...ux.vnet.ibm.com, keescook@...omium.org,
        Jessica Yu <jeyu@...nel.org>,
        kernel-hardening@...ts.openwall.com, kernel-team@...roid.com,
        mathieu.desnoyers@...icios.com, rcu@...r.kernel.org,
        rostedt@...dmis.org
Subject: [PATCH 2/2] module: Make srcu_struct ptr array as read-only post init

Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in
modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array
of srcu_struct pointers which is used by srcu code to initialize and
clean up these structures.

There is no reason for this array of pointers to be writable, and can
cause security or other hidden bugs. Mark these are read-only after the
module init has completed.

Suggested-by: paulmck@...ux.vnet.ibm.com
Suggested-by: keescook@...omium.org
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>

---
 kernel/module.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
index f9221381d076..ed1f2612aebc 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3301,7 +3301,7 @@ static bool blacklisted(const char *module_name)
 core_param(module_blacklist, module_blacklist, charp, 0400);
 
 /*
- * Mark ro_after_init section with SHF_RO_AFTER_INIT so that
+ * These are section names marked with SHF_RO_AFTER_INIT so that
  * layout_sections() can put it in the right place.
  * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
  */
@@ -3314,6 +3314,13 @@ static char *ro_after_init_sections[] = {
 	 * annotated as such at module load time.
 	 */
 	"__jump_table",
+
+	/*
+	 * Used for SRCU structures which need to be initialized/cleaned up
+	 * by the SRCU notifiers
+	 */
+	"___srcu_struct_ptrs",
+
 	NULL
 };
 
-- 
2.21.0.392.gf8f6787159e-goog