[PATCH 09/12] rodata_test: add verification for __wr_after_init

From: Igor Stoppa <igor.stoppa@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>,
	Matthew Wilcox <willy@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: igor.stoppa@huawei.com, Nadav Amit <nadav.amit@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	linux-integrity@vger.kernel.org,
	kernel-hardening@lists.openwall.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 09/12] rodata_test: add verification for __wr_after_init
Date: Wed, 19 Dec 2018 23:33:35 +0200	[thread overview]
Message-ID: <20181219213338.26619-10-igor.stoppa@huawei.com> (raw)
In-Reply-To: <20181219213338.26619-1-igor.stoppa@huawei.com>

The write protection of the __wr_after_init data can be verified with the
same methodology used for const data.

Signed-off-by: Igor Stoppa <igor.stoppa@huawei.com>

CC: Andy Lutomirski <luto@amacapital.net>
CC: Nadav Amit <nadav.amit@gmail.com>
CC: Matthew Wilcox <willy@infradead.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Kees Cook <keescook@chromium.org>
CC: Dave Hansen <dave.hansen@linux.intel.com>
CC: Mimi Zohar <zohar@linux.vnet.ibm.com>
CC: linux-integrity@vger.kernel.org
CC: kernel-hardening@lists.openwall.com
CC: linux-mm@kvack.org
CC: linux-kernel@vger.kernel.org
---
 mm/rodata_test.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/mm/rodata_test.c b/mm/rodata_test.c
index e1349520b436..a669cf9f5a61 100644
--- a/mm/rodata_test.c
+++ b/mm/rodata_test.c
@@ -16,8 +16,23 @@
 
 #define INIT_TEST_VAL 0xC3
 
+/*
+ * Note: __ro_after_init data is, for every practical effect, equivalent to
+ * const data, since they are even write protected at the same time; there
+ * is no need for separate testing.
+ * __wr_after_init data, otoh, is altered also after the write protection
+ * takes place and it cannot be exploitable for altering more permanent
+ * data.
+ */
+
 static const int rodata_test_data = INIT_TEST_VAL;
 
+#ifdef CONFIG_PRMEM
+static int wr_after_init_test_data __wr_after_init = INIT_TEST_VAL;
+extern long __start_wr_after_init;
+extern long __end_wr_after_init;
+#endif
+
 static bool test_data(char *data_type, const int *data,
 		      unsigned long start, unsigned long end)
 {
@@ -59,7 +74,13 @@ static bool test_data(char *data_type, const int *data,
 
 void rodata_test(void)
 {
-	test_data("rodata", &rodata_test_data,
-		  (unsigned long)&__start_rodata,
-		  (unsigned long)&__end_rodata);
+	if (!test_data("rodata", &rodata_test_data,
+		       (unsigned long)&__start_rodata,
+		       (unsigned long)&__end_rodata))
+		return;
+#ifdef CONFIG_PRMEM
+	    test_data("wr after init data", &wr_after_init_test_data,
+		      (unsigned long)&__start_wr_after_init,
+		      (unsigned long)&__end_wr_after_init);
+#endif
 }
-- 
2.19.1

