[PATCH] selftests/bpf: Add arena direct-value boundary test

[Dhiraj Shah <find.dhiraj@gmail.com>]

Add coverage for direct map value access against BPF_MAP_TYPE_ARENA.
For a one-page arena, an offset of PAGE_SIZE - 1 is valid, while
PAGE_SIZE is one byte past the end of the mapping and must be rejected.

This covers the off-by-one case in arena direct-value range checking.

Signed-off-by: Dhiraj Shah <find.dhiraj@gmail.com>
---
 .../bpf/prog_tests/arena_direct_value.c       | 65 +++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_direct_value.c

diff --git a/tools/testing/selftests/bpf/prog_tests/arena_direct_value.c b/tools/testing/selftests/bpf/prog_tests/arena_direct_value.c
new file mode 100644
index 000000000000..00e65af5df6c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/arena_direct_value.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include <bpf/bpf.h>
+#include <linux/filter.h>
+#include <sys/mman.h>
+#include <sys/user.h>
+#ifndef PAGE_SIZE
+#include <unistd.h>
+#define PAGE_SIZE getpagesize()
+#endif
+
+static int create_arena(void)
+{
+	LIBBPF_OPTS(bpf_map_create_opts, opts,
+		    .map_flags = BPF_F_MMAPABLE,
+	);
+
+	return bpf_map_create(BPF_MAP_TYPE_ARENA, "arena", 0, 0, 1, &opts);
+}
+
+static int load_direct_value_prog(int map_fd, int off)
+{
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, map_fd, off),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+
+	return bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL",
+			     insns, ARRAY_SIZE(insns), NULL);
+}
+
+static void test_direct_value_boundary(void)
+{
+	void *area = MAP_FAILED;
+	int map_fd, prog_fd;
+
+	map_fd = create_arena();
+	if (!ASSERT_OK_FD(map_fd, "create_arena"))
+		return;
+
+	area = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, map_fd, 0);
+	if (!ASSERT_NEQ(area, MAP_FAILED, "arena_mmap"))
+		goto out;
+
+	prog_fd = load_direct_value_prog(map_fd, PAGE_SIZE - 1);
+	if (ASSERT_OK_FD(prog_fd, "last_valid_byte"))
+		close(prog_fd);
+
+	prog_fd = load_direct_value_prog(map_fd, PAGE_SIZE);
+	if (!ASSERT_LT(prog_fd, 0, "one_past_end"))
+		close(prog_fd);
+
+out:
+	if (area != MAP_FAILED)
+		munmap(area, PAGE_SIZE);
+	close(map_fd);
+}
+
+void test_arena_direct_value(void)
+{
+	if (test__start_subtest("direct_value_boundary"))
+		test_direct_value_boundary();
+}
-- 
2.43.0