[PATCH 1/4] selftests/sgx: Fix segfault upon early test failure

[Reinette Chatre <reinette.chatre@intel.com>]

A segfault is encountered if there happens to be an
early failure of any of the SGX tests. One way to
reproduce this is to remove the enclave binary
"test_encl.elf" that will trigger early enclave loading
failure followed by a segfault.

The segfault occurs within encl_delete() that cleans up
after an enclave by umapping its mapped regions and closing
the file descriptor to the SGX driver. As integrated with
the kselftest harness encl_delete() is called upon exit
from every test, irrespective of test success. encl_delete()
is also called to clean up if an error is encountered during
enclave loading.

encl_delete() is thus responsible for cleaning any amount of
enclave state - including state that has already been cleaned.

encl_delete() starts by accessing encl->segment_tbl that may
not have been created yet due to a very early failure or may
already be cleaned up because of a failure encountered after
encl->segment_tbl was created.

Ensure encl->segment_tbl is valid before attempting to access
memory offset from it. The offset with which it is accessed,
encl->nr_segments, is initialized after encl->segment_tbl and
thus considered valid to use after the encl->segment_tbl check
succeeds.

Fixes: 3200505d4de6 ("selftests/sgx: Create a heap for the test enclave")
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
 tools/testing/selftests/sgx/load.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/sgx/load.c b/tools/testing/selftests/sgx/load.c
index 9d4322c946e2..006b464c8fc9 100644
--- a/tools/testing/selftests/sgx/load.c
+++ b/tools/testing/selftests/sgx/load.c
@@ -21,7 +21,7 @@
 
 void encl_delete(struct encl *encl)
 {
-	struct encl_segment *heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
+	struct encl_segment *heap_seg;
 
 	if (encl->encl_base)
 		munmap((void *)encl->encl_base, encl->encl_size);
@@ -32,10 +32,11 @@ void encl_delete(struct encl *encl)
 	if (encl->fd)
 		close(encl->fd);
 
-	munmap(heap_seg->src, heap_seg->size);
-
-	if (encl->segment_tbl)
+	if (encl->segment_tbl) {
+		heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
+		munmap(heap_seg->src, heap_seg->size);
 		free(encl->segment_tbl);
+	}
 
 	memset(encl, 0, sizeof(*encl));
 }
-- 
2.25.1