[RFC PATCH v1 2/2] selftests/memfd: Add tests for F_SEAL_FUTURE_EXEC

["Isaac J. Manjarres" <isaacmanjarres@google.com>]

Add tests to ensure that F_SEAL_FUTURE_EXEC behaves as expected.

Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: John Stultz <jstultz@google.com>
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
---
 tools/testing/selftests/memfd/memfd_test.c | 79 ++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 46027c889e74..12c82af406b3 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -30,6 +30,7 @@
 #define STACK_SIZE 65536
 
 #define F_SEAL_EXEC	0x0020
+#define F_SEAL_FUTURE_EXEC	0x0040
 
 #define F_WX_SEALS (F_SEAL_SHRINK | \
 		    F_SEAL_GROW | \
@@ -317,6 +318,37 @@ static void *mfd_assert_mmap_private(int fd)
 	return p;
 }
 
+static void *mfd_fail_mmap_exec(int fd)
+{
+	void *p;
+
+	p = mmap(NULL,
+		 mfd_def_size,
+		 PROT_EXEC,
+		 MAP_SHARED,
+		 fd,
+		 0);
+	if (p != MAP_FAILED) {
+		printf("mmap() didn't fail as expected\n");
+		abort();
+	}
+
+	return p;
+}
+
+static void mfd_fail_mprotect_exec(void *p)
+{
+	int ret;
+
+	ret = mprotect(p,
+		       mfd_def_size,
+		       PROT_EXEC);
+	if (!ret) {
+		printf("mprotect didn't fail as expected\n");
+		abort();
+	}
+}
+
 static int mfd_assert_open(int fd, int flags, mode_t mode)
 {
 	char buf[512];
@@ -997,6 +1029,52 @@ static void test_seal_future_write(void)
 	close(fd);
 }
 
+/*
+ * Test SEAL_FUTURE_EXEC_MAPPING
+ * Test whether SEAL_FUTURE_EXEC_MAPPING actually prevents executable mappings.
+ */
+static void test_seal_future_exec_mapping(void)
+{
+	int fd;
+	void *p;
+
+
+	printf("%s SEAL-FUTURE-EXEC-MAPPING\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_future_exec_mapping",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	/*
+	 * PROT_READ | PROT_WRITE mappings create VMAs with VM_MAYEXEC set.
+	 * However, F_SEAL_FUTURE_EXEC applies to subsequent mappings,
+	 * so it should still succeed even if this mapping is active when the
+	 * seal is applied.
+	 */
+	p = mfd_assert_mmap_shared(fd);
+
+	mfd_assert_has_seals(fd, 0);
+
+	mfd_assert_add_seals(fd, F_SEAL_FUTURE_EXEC);
+	mfd_assert_has_seals(fd, F_SEAL_FUTURE_EXEC);
+
+	mfd_fail_mmap_exec(fd);
+
+	munmap(p, mfd_def_size);
+
+	/* Ensure that new mappings without PROT_EXEC work. */
+	p = mfd_assert_mmap_shared(fd);
+
+	/*
+	 * Ensure that mappings created after the seal was applied cannot be
+	 * made executable via mprotect().
+	 */
+	mfd_fail_mprotect_exec(p);
+
+	munmap(p, mfd_def_size);
+	close(fd);
+}
+
 static void test_seal_write_map_read_shared(void)
 {
 	int fd;
@@ -1633,6 +1711,7 @@ int main(int argc, char **argv)
 	test_seal_shrink();
 	test_seal_grow();
 	test_seal_resize();
+	test_seal_future_exec_mapping();
 
 	test_sysctl_simple();
 	test_sysctl_nested();
-- 
2.47.0.338.g60cca15819-goog