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bpf: properly verify tail call behavior #6282

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bpf: properly verify tail call behavior #6282

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25 changes: 22 additions & 3 deletions kernel/bpf/verifier.c
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Original file line number Diff line number Diff line change
Expand Up @@ -10974,6 +10974,10 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
bool in_callback_fn;
int err;

err = bpf_update_live_stack(env);
if (err)
return err;

callee = state->frame[state->curframe];
r0 = &callee->regs[BPF_REG_0];
if (r0->type == PTR_TO_STACK) {
Expand Down Expand Up @@ -11884,6 +11888,24 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
env->prog->call_get_func_ip = true;
}

if (func_id == BPF_FUNC_tail_call) {
if (env->cur_state->curframe) {
struct bpf_verifier_state *branch;
mark_reg_scratched(env, BPF_REG_0);
branch = push_stack(env, env->insn_idx + 1, env->insn_idx, false);
if (IS_ERR(branch))
return PTR_ERR(branch);
clear_all_pkt_pointers(env);
mark_reg_unknown(env, regs, BPF_REG_0);
err = prepare_func_exit(env, &env->insn_idx);
if (err)
return err;
env->insn_idx--;
} else {
changes_data = false;
}
}

if (changes_data)
clear_all_pkt_pointers(env);
return 0;
Expand Down Expand Up @@ -19782,9 +19804,6 @@ static int process_bpf_exit_full(struct bpf_verifier_env *env,
return PROCESS_BPF_EXIT;

if (env->cur_state->curframe) {
err = bpf_update_live_stack(env);
if (err)
return err;
/* exit from nested function */
err = prepare_func_exit(env, &env->insn_idx);
if (err)
Expand Down
39 changes: 37 additions & 2 deletions tools/testing/selftests/bpf/progs/verifier_sock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1117,10 +1117,17 @@ int tail_call(struct __sk_buff *sk)
return 0;
}

/* Tail calls invalidate packet pointers. */
static __noinline
int static_tail_call(struct __sk_buff *sk)
{
bpf_tail_call_static(sk, &jmp_table, 0);
return 0;
}

/* Tail calls in sub-programs invalidate packet pointers. */
SEC("tc")
__failure __msg("invalid mem access")
int invalidate_pkt_pointers_by_tail_call(struct __sk_buff *sk)
int invalidate_pkt_pointers_by_global_tail_call(struct __sk_buff *sk)
{
int *p = (void *)(long)sk->data;

Expand All @@ -1131,4 +1138,32 @@ int invalidate_pkt_pointers_by_tail_call(struct __sk_buff *sk)
return TCX_PASS;
}

/* Tail calls in static sub-programs invalidate packet pointers. */
SEC("tc")
__failure __msg("invalid mem access")
int invalidate_pkt_pointers_by_static_tail_call(struct __sk_buff *sk)
{
int *p = (void *)(long)sk->data;

if ((void *)(p + 1) > (void *)(long)sk->data_end)
return TCX_DROP;
static_tail_call(sk);
*p = 42; /* this is unsafe */
return TCX_PASS;
}

/* Direct tail calls do not invalidate packet pointers. */
SEC("tc")
__success
int invalidate_pkt_pointers_by_tail_call(struct __sk_buff *sk)
{
int *p = (void *)(long)sk->data;

if ((void *)(p + 1) > (void *)(long)sk->data_end)
return TCX_DROP;
bpf_tail_call_static(sk, &jmp_table, 0);
*p = 42; /* this is NOT unsafe: tail calls don't return */
return TCX_PASS;
}

char _license[] SEC("license") = "GPL";
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