tailcall_fail.c

 1// SPDX-License-Identifier: GPL-2.0
 2/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
 3#include <vmlinux.h>
 4#include <bpf/bpf_tracing.h>
 5#include <bpf/bpf_helpers.h>
 6#include <bpf/bpf_core_read.h>
 7
 8#include "bpf_misc.h"
 9#include "bpf_experimental.h"
10
11extern void bpf_rcu_read_lock(void) __ksym;
12extern void bpf_rcu_read_unlock(void) __ksym;
13
14#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
15
16private(A) struct bpf_spin_lock lock;
17
18struct {
19	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
20	__uint(max_entries, 3);
21	__uint(key_size, sizeof(__u32));
22	__uint(value_size, sizeof(__u32));
23} jmp_table SEC(".maps");
24
25SEC("?tc")
26__failure __msg("function calls are not allowed while holding a lock")
27int reject_tail_call_spin_lock(struct __sk_buff *ctx)
28{
29	bpf_spin_lock(&lock);
30	bpf_tail_call_static(ctx, &jmp_table, 0);
31	return 0;
32}
33
34SEC("?tc")
35__failure __msg("tail_call cannot be used inside bpf_rcu_read_lock-ed region")
36int reject_tail_call_rcu_lock(struct __sk_buff *ctx)
37{
38	bpf_rcu_read_lock();
39	bpf_tail_call_static(ctx, &jmp_table, 0);
40	bpf_rcu_read_unlock();
41	return 0;
42}
43
44SEC("?tc")
45__failure __msg("tail_call cannot be used inside bpf_preempt_disable-ed region")
46int reject_tail_call_preempt_lock(struct __sk_buff *ctx)
47{
48	bpf_guard_preempt();
49	bpf_tail_call_static(ctx, &jmp_table, 0);
50	return 0;
51}
52
53SEC("?tc")
54__failure __msg("tail_call would lead to reference leak")
55int reject_tail_call_ref(struct __sk_buff *ctx)
56{
57	struct foo { int i; } *p;
58
59	p = bpf_obj_new(typeof(*p));
60	bpf_tail_call_static(ctx, &jmp_table, 0);
61	return 0;
62}
63
64char _license[] SEC("license") = "GPL";