[PATCH v3 2/2] selftest: use mmap instead of posix_memalign to allocate memory

[Peter Collingbourne]

This test passes pointers obtained from anon_allocate_area to the
userfaultfd and mremap APIs. This causes a problem if the system
allocator returns tagged pointers because with the tagged address ABI
the kernel rejects tagged addresses passed to these APIs, which would
end up causing the test to fail. To make this test compatible with
such system allocators, stop using the system allocator to allocate
memory in anon_allocate_area, and instead just use mmap.

Co-developed-by: Lokesh Gidra <lokeshgidra at google.com>
Signed-off-by: Lokesh Gidra <lokeshgidra at google.com>
Signed-off-by: Peter Collingbourne <pcc at google.com>
Fixes: c47174fc362a ("userfaultfd: selftest")
Cc: <stable at vger.kernel.org> # 5.4
Link: https://linux-review.googlesource.com/id/Icac91064fcd923f77a83e8e133f8631c5b8fc241
---
 tools/testing/selftests/vm/userfaultfd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index f5ab5e0312e7..d0f802053dfd 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -197,8 +197,10 @@ static int anon_release_pages(char *rel_area)
 
 static void anon_allocate_area(void **alloc_area)
 {
-	if (posix_memalign(alloc_area, page_size, nr_pages * page_size)) {
-		fprintf(stderr, "out of memory\n");
+	*alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
+			   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (*alloc_area == MAP_FAILED) {
+		fprintf(stderr, "anon memory mmap failed\n");
 		*alloc_area = NULL;
 	}
 }
-- 
2.32.0.93.g670b81a890-goog