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

Isaac J. Manjarres
2024-12-06T01:09:44Z

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