selftests/bpf: Add test for sleepable bpf iterator programs

This adds a test for bpf iterator programs to make use of sleepable
bpf helpers.

Signed-off-by: Kenny Yu <kennyyu@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220124185403.468466-5-kennyyu@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/bpf_iter.c

@@ -138,6 +138,24 @@ static void test_task(void)
 	bpf_iter_task__destroy(skel);
 }
 
+static void test_task_sleepable(void)
+{
+	struct bpf_iter_task *skel;
+
+	skel = bpf_iter_task__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "bpf_iter_task__open_and_load"))
+		return;
+
+	do_dummy_read(skel->progs.dump_task_sleepable);
+
+	ASSERT_GT(skel->bss->num_expected_failure_copy_from_user_task, 0,
+		  "num_expected_failure_copy_from_user_task");
+	ASSERT_GT(skel->bss->num_success_copy_from_user_task, 0,
+		  "num_success_copy_from_user_task");
+
+	bpf_iter_task__destroy(skel);
+}
+
 static void test_task_stack(void)
 {
 	struct bpf_iter_task_stack *skel;
@@ -1252,6 +1270,8 @@ void test_bpf_iter(void)
 		test_bpf_map();
 	if (test__start_subtest("task"))
 		test_task();
+	if (test__start_subtest("task_sleepable"))
+		test_task_sleepable();
 	if (test__start_subtest("task_stack"))
 		test_task_stack();
 	if (test__start_subtest("task_file"))

tools/testing/selftests/bpf/progs/bpf_iter_task.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2020 Facebook */
 #include "bpf_iter.h"
 #include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
 
 char _license[] SEC("license") = "GPL";
 
@@ -23,3 +24,56 @@ int dump_task(struct bpf_iter__task *ctx)
 	BPF_SEQ_PRINTF(seq, "%8d %8d\n", task->tgid, task->pid);
 	return 0;
 }
+
+int num_expected_failure_copy_from_user_task = 0;
+int num_success_copy_from_user_task = 0;
+
+SEC("iter.s/task")
+int dump_task_sleepable(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	static const char info[] = "    === END ===";
+	struct pt_regs *regs;
+	void *ptr;
+	uint32_t user_data = 0;
+	int ret;
+
+	if (task == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+
+	/* Read an invalid pointer and ensure we get an error */
+	ptr = NULL;
+	ret = bpf_copy_from_user_task(&user_data, sizeof(uint32_t), ptr, task, 0);
+	if (ret) {
+		++num_expected_failure_copy_from_user_task;
+	} else {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+
+	/* Try to read the contents of the task's instruction pointer from the
+	 * remote task's address space.
+	 */
+	regs = (struct pt_regs *)bpf_task_pt_regs(task);
+	if (regs == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+	ptr = (void *)PT_REGS_IP(regs);
+
+	ret = bpf_copy_from_user_task(&user_data, sizeof(uint32_t), ptr, task, 0);
+	if (ret) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+	++num_success_copy_from_user_task;
+
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "    tgid      gid     data\n");
+
+	BPF_SEQ_PRINTF(seq, "%8d %8d %8d\n", task->tgid, task->pid, user_data);
+	return 0;
+}