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From:   Rick Edgecombe <rick.p.edgecombe@intel.com>
To:     Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Nadav Amit <nadav.amit@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>, linux_dti@icloud.com,
        linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org, akpm@linux-foundation.org,
        kernel-hardening@lists.openwall.com, linux-mm@kvack.org,
        will.deacon@arm.com, ard.biesheuvel@linaro.org,
        kristen@linux.intel.com, deneen.t.dock@intel.com,
        Nadav Amit <namit@vmware.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>
Subject: [PATCH 17/17] module: Prevent module removal racing with text_poke()
Date:   Wed, 16 Jan 2019 16:32:59 -0800
Message-Id: <20190117003259.23141-18-rick.p.edgecombe@intel.com>
In-Reply-To: <20190117003259.23141-1-rick.p.edgecombe@intel.com>
References: <20190117003259.23141-1-rick.p.edgecombe@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Nadav Amit <namit@vmware.com>

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@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 kernel/module.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index 1af5c8e19086..90cfc4988d98 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"
 
@@ -2157,6 +2158,9 @@ static void free_module(struct module *mod)
 	synchronize_rcu();
 	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_arch_freeing_init(mod);
 	module_memfree(mod->init_layout.base);
@@ -2168,6 +2172,7 @@ static void free_module(struct module *mod)
 
 	/* Finally, free the core (containing the module structure) */
 	module_memfree(mod->core_layout.base);
+	mutex_unlock(&text_mutex);
 }
 
 void *__symbol_get(const char *symbol)
-- 
2.17.1