[PATCH v3 bpf-next] selftests/bpf: add tests for arena vma split and fork

[Ruslan Valiyev <linuxoid@gmail.com>]

Add a test that an arena map's mmap()ed region cannot be split by a
partial munmap() (the "split" subtest, which expects -EINVAL) and is not
inherited across fork() (the "fork" subtest, where mincore() reports the
child's range as unmapped).

Signed-off-by: Ruslan Valiyev <linuxoid@gmail.com>
---
v3:
- Consolidate into one file with a shared setup helper and two
  subtests.
- Put the opening /* of the multi-line comment on its own line.
v2:
- Drop the regression-test framing and per-callback details.
- Split the original single test; unpack the mincore() check.

 .../selftests/bpf/prog_tests/arena_vma.c      | 94 +++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_vma.c

diff --git a/tools/testing/selftests/bpf/prog_tests/arena_vma.c b/tools/testing/selftests/bpf/prog_tests/arena_vma.c
new file mode 100644
index 0000000000000..f6c07cd31d08b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/arena_vma.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <errno.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+/* Make sure arena mappings cannot be split or inherited. */
+
+#define NR_PAGES 3
+
+static int arena_mmap(int *fd, void **area, size_t *sz)
+{
+	LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_MMAPABLE);
+
+	*sz = (size_t)NR_PAGES * sysconf(_SC_PAGESIZE);
+
+	*fd = bpf_map_create(BPF_MAP_TYPE_ARENA, "arena_vma", 0, 0, NR_PAGES, &opts);
+	if (!ASSERT_OK_FD(*fd, "arena map create"))
+		return -1;
+
+	*area = mmap(NULL, *sz, PROT_READ | PROT_WRITE, MAP_SHARED, *fd, 0);
+	if (!ASSERT_NEQ(*area, MAP_FAILED, "mmap arena")) {
+		close(*fd);
+		return -1;
+	}
+	return 0;
+}
+
+/* A partial munmap that would split the arena mapping must be rejected. */
+static void split_test(void)
+{
+	long ps = sysconf(_SC_PAGESIZE);
+	void *area;
+	size_t sz;
+	int fd, ret, err;
+
+	if (arena_mmap(&fd, &area, &sz))
+		return;
+
+	ret = munmap((char *)area + ps, ps);
+	err = errno;
+	if (ASSERT_ERR(ret, "split munmap"))
+		ASSERT_EQ(err, EINVAL, "split munmap errno");
+
+	munmap(area, sz);
+	close(fd);
+}
+
+/* A forked child must not inherit the arena mapping. */
+static void fork_test(void)
+{
+	long ps = sysconf(_SC_PAGESIZE);
+	void *area;
+	size_t sz;
+	int fd, ret, status;
+	pid_t pid;
+
+	if (arena_mmap(&fd, &area, &sz))
+		return;
+
+	pid = fork();
+	if (pid == 0) {
+		unsigned char vec;
+		int rc;
+
+		/*
+		 * If the mapping was not inherited the range is unmapped in
+		 * the child, so mincore() fails with ENOMEM. A success means
+		 * the child wrongly inherited the mapping.
+		 */
+		rc = mincore(area, ps, &vec);
+		if (rc == 0)
+			_exit(1);
+		_exit(errno == ENOMEM ? 0 : 2);
+	}
+	if (ASSERT_GE(pid, 0, "fork")) {
+		while ((ret = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
+			;
+		if (ASSERT_EQ(ret, pid, "waitpid"))
+			ASSERT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0,
+				    "child must not inherit arena mapping");
+	}
+
+	munmap(area, sz);
+	close(fd);
+}
+
+void test_arena_vma(void)
+{
+	if (test__start_subtest("split"))
+		split_test();
+	if (test__start_subtest("fork"))
+		fork_test();
+}

base-commit: 174914ea551314c52a61713b9c4bde9e42d48073
-- 
2.43.0