linux-kernel - [PATCH v7 14/14] module: Prevent module removal racing with text

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Date:   Tue, 4 Dec 2018 17:34:08 -0800
From:   Nadav Amit <namit@...are.com>
To:     Ingo Molnar <mingo@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>, <linux_dti@...oud.com>,
        <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        Nadav Amit <namit@...are.com>
Subject: [PATCH v7 14/14] module: Prevent module removal racing with text_poke()

It seems dangerous to allow code modifications to take place
concurrently with module unloading. So take the text_mutex while the
memory of the module is freed.

Signed-off-by: Nadav Amit <namit@...are.com>
---
 kernel/module.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index 57c5b23746e7..b45754961143 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,6 +64,7 @@
 #include <linux/bsearch.h>
 #include <linux/dynamic_debug.h>
 #include <linux/audit.h>
+#include <linux/memory.h>
 #include <uapi/linux/module.h>
 #include "module-internal.h"
 
@@ -2181,6 +2182,9 @@ static void free_module(struct module *mod)
 	synchronize_sched();
 	mutex_unlock(&module_mutex);
 
+	/* Protect against patching of the module while it is being removed */
+	mutex_lock(&text_mutex);
+
 	/* This may be empty, but that's OK */
 	module_restore_mappings(&mod->init_layout);
 	module_arch_freeing_init(mod);
@@ -2194,6 +2198,7 @@ static void free_module(struct module *mod)
 	/* Finally, free the core (containing the module structure) */
 	module_restore_mappings(&mod->core_layout);
 	module_memfree(mod->core_layout.base);
+	mutex_unlock(&text_mutex);
 }
 
 void *__symbol_get(const char *symbol)
-- 
2.17.1