selftests/mm: add mseal test for no-discard madvise

Add an mseal test for madvise() operations that aren't considered
"discard" (e.g purely advisory ops such as MADV_RANDOM).

[pedro.falcato@gmail.com: adjust the mseal test's plan]
  Link: https://lkml.kernel.org/r/20240807203724.2686144-1-pedro.falcato@gmail.com
Link: https://lkml.kernel.org/r/20240807173336.2523757-3-pedro.falcato@gmail.comSigned-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Tested-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Jeff Xu <jeffxu@chromium.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/mseal_test.c

@@ -1731,6 +1731,38 @@ static void test_seal_discard_ro_anon(bool seal)
 	REPORT_TEST_PASS();
 }
 
+static void test_seal_madvise_nodiscard(bool seal)
+{
+	void *ptr;
+	unsigned long page_size = getpagesize();
+	unsigned long size = 4 * page_size;
+	int ret;
+
+	setup_single_address(size, &ptr);
+	FAIL_TEST_IF_FALSE(ptr != (void *)-1);
+
+	if (seal) {
+		ret = seal_single_address(ptr, size);
+		FAIL_TEST_IF_FALSE(!ret);
+	}
+
+	/*
+	 * Test a random madvise flag like MADV_RANDOM that does not touch page
+	 * contents (and thus should work for msealed VMAs). RANDOM also happens to
+	 * share bits with other discard-ish flags like REMOVE.
+	 */
+	ret = sys_madvise(ptr, size, MADV_RANDOM);
+	FAIL_TEST_IF_FALSE(!ret);
+
+	ret = sys_munmap(ptr, size);
+	if (seal)
+		FAIL_TEST_IF_FALSE(ret < 0);
+	else
+		FAIL_TEST_IF_FALSE(!ret);
+
+	REPORT_TEST_PASS();
+}
+
 int main(int argc, char **argv)
 {
 	bool test_seal = seal_support();
@@ -1743,7 +1775,7 @@ int main(int argc, char **argv)
 	if (!pkey_supported())
 		ksft_print_msg("PKEY not supported\n");
 
-	ksft_set_plan(80);
+	ksft_set_plan(82);
 
 	test_seal_addseal();
 	test_seal_unmapped_start();
@@ -1822,6 +1854,8 @@ int main(int argc, char **argv)
 	test_seal_mremap_move_fixed_zero(true);
 	test_seal_mremap_move_dontunmap_anyaddr(false);
 	test_seal_mremap_move_dontunmap_anyaddr(true);
+	test_seal_madvise_nodiscard(false);
+	test_seal_madvise_nodiscard(true);
 	test_seal_discard_ro_anon(false);
 	test_seal_discard_ro_anon(true);
 	test_seal_discard_ro_anon_on_rw(false);