[PATCH v3 1/3] module: Prepare for addition of new ro_after_init sections

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
	paulmck@linux.vnet.ibm.com, rostedt@goodmis.org,
	mathieu.desnoyers@efficios.com, rcu@vger.kernel.org,
	kernel-hardening@lists.openwall.com, kernel-team@android.com,
	keescook@chromium.org, Jessica Yu <jeyu@kernel.org>
Subject: [PATCH v3 1/3] module: Prepare for addition of new ro_after_init sections
Date: Wed, 10 Apr 2019 15:57:06 -0400	[thread overview]
Message-ID: <20190410195708.162185-1-joel@joelfernandes.org> (raw)

For the purposes of hardening modules by adding sections to
ro_after_init sections, prepare for addition of new ro_after_init
entries which we do in future patches. Create a table to which new
entries could be added later. This makes it less error prone and reduce
code duplication.

Cc: paulmck@linux.vnet.ibm.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: rcu@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: kernel-team@android.com
Suggested-by: keescook@chromium.org
Reviewed-by: keescook@chromium.org
Acked-by: rostedt@goodmis.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

---
 kernel/module.c | 41 +++++++++++++++++++++++------------------
 1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 524da609c884..42e4e289d6c7 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3300,11 +3300,27 @@ 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
+ * layout_sections() can put it in the right place.
+ * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
+ */
+static const char * const ro_after_init_sections[] = {
+	".data..ro_after_init",
+
+	/*
+	 * __jump_table structures are never modified, with the exception of
+	 * entries that refer to code in the __init section, which are
+	 * annotated as such at module load time.
+	 */
+	"__jump_table",
+};
+
 static struct module *layout_and_allocate(struct load_info *info, int flags)
 {
 	struct module *mod;
 	unsigned int ndx;
-	int err;
+	int err, i;
 
 	err = check_modinfo(info->mod, info, flags);
 	if (err)
@@ -3319,23 +3335,12 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 	/* We will do a special allocation for per-cpu sections later. */
 	info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;
 
-	/*
-	 * Mark ro_after_init section 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.
-	 */
-	ndx = find_sec(info, ".data..ro_after_init");
-	if (ndx)
-		info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
-	/*
-	 * Mark the __jump_table section as ro_after_init as well: these data
-	 * structures are never modified, with the exception of entries that
-	 * refer to code in the __init section, which are annotated as such
-	 * at module load time.
-	 */
-	ndx = find_sec(info, "__jump_table");
-	if (ndx)
-		info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+	/* Set sh_flags for read-only after init sections */
+	for (i = 0; i < ARRAY_SIZE(ro_after_init_sections); i++) {
+		ndx = find_sec(info, ro_after_init_sections[i]);
+		if (ndx)
+			info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+	}
 
 	/* Determine total sizes, and put offsets in sh_entsize.  For now
 	   this is done generically; there doesn't appear to be any
-- 
2.21.0.392.gf8f6787159e-goog

