selftests/bpf: Add test for early update in prog_array_map_poke_run

Adding test that tries to trigger the BUG_IN during early map update
in prog_array_map_poke_run function.

The idea is to share prog array map between thread that constantly
updates it and another one loading a program that uses that prog
array.

Eventually we will hit a place where the program is ok to be updated
(poke->tailcall_target_stable check) but the address is still not
registered in kallsyms, so the bpf_arch_text_poke returns -EINVAL
and cause imbalance for the next tail call update check, which will
fail with -EBUSY in bpf_arch_text_poke as described in previous fix.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20231206083041.1306660-3-jolsa@kernel.org

1 files changed, 32 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/tailcall_poke.c b/tools/testing/selftests/bpf/progs/tailcall_poke.c
new file mode 100644
index 000000000000..c78b94b75e83
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tailcall_poke.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} jmp_table SEC(".maps");
+
+SEC("?fentry/bpf_fentry_test1")
+int BPF_PROG(test, int a)
+{
+	bpf_tail_call_static(ctx, &jmp_table, 0);
+	return 0;
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(call1, int a)
+{
+	return 0;
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(call2, int a)
+{
+	return 0;
+}