We hit following issues [1] [2] when we attach bpf program that calls bpf_trace_printk helper to the contention_begin tracepoint. As described in [3] with multiple bpf programs that call bpf_trace_printk helper attached to the contention_begin might result in exhaustion of printk buffer or cause a deadlock [2]. There's also another possible deadlock when multiple bpf programs attach to bpf_trace_printk tracepoint and call one of the printk bpf helpers. This change denies the attachment of bpf program to contention_begin and bpf_trace_printk tracepoints if the bpf program calls one of the printk bpf helpers. Adding also verifier check for tb_btf programs, so this can be cought in program loading time with error message like: Can't attach program with bpf_trace_printk#6 helper to contention_begin tracepoint. [1] https://lore.kernel.org/bpf/CACkBjsakT_yWxnSWr4r-0TpPvbKm9-OBmVUhJb7hV3hY8fdCkw@xxxxxxxxxxxxxx/ [2] https://lore.kernel.org/bpf/CACkBjsaCsTovQHFfkqJKto6S4Z8d02ud1D7MPESrHa1cVNNTrw@xxxxxxxxxxxxxx/ [3] https://lore.kernel.org/bpf/Y2j6ivTwFmA0FtvY@krava/ Reported-by: Hao Sun <sunhao.th@xxxxxxxxx> Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> --- include/linux/bpf.h | 1 + include/linux/bpf_verifier.h | 2 ++ kernel/bpf/syscall.c | 3 +++ kernel/bpf/verifier.c | 46 ++++++++++++++++++++++++++++++++++++ 4 files changed, 52 insertions(+) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c9eafa67f2a2..3ccabede0f50 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1319,6 +1319,7 @@ struct bpf_prog { enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */ call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */ call_get_func_ip:1, /* Do we call get_func_ip() */ + call_printk:1, /* Do we call trace_printk/trace_vprintk */ tstamp_type_access:1; /* Accessed __sk_buff->tstamp_type */ enum bpf_prog_type type; /* Type of BPF program */ enum bpf_attach_type expected_attach_type; /* For some prog types */ diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 545152ac136c..7118c2fda59d 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -618,6 +618,8 @@ bool is_dynptr_type_expected(struct bpf_verifier_env *env, struct bpf_reg_state *reg, enum bpf_arg_type arg_type); +int bpf_check_tp_printk_denylist(const char *name, struct bpf_prog *prog); + /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */ static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog, struct btf *btf, u32 btf_id) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 35972afb6850..9a69bda7d62b 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3329,6 +3329,9 @@ static int bpf_raw_tp_link_attach(struct bpf_prog *prog, return -EINVAL; } + if (bpf_check_tp_printk_denylist(tp_name, prog)) + return -EACCES; + btp = bpf_get_raw_tracepoint(tp_name); if (!btp) return -ENOENT; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f07bec227fef..b662bc851e1c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7472,6 +7472,47 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno state->callback_subprogno == subprogno); } +int bpf_check_tp_printk_denylist(const char *name, struct bpf_prog *prog) +{ + static const char * const denylist[] = { + "contention_begin", + "bpf_trace_printk", + }; + int i; + + /* Do not allow attachment to denylist[] tracepoints, + * if the program calls some of the printk helpers, + * because there's possibility of deadlock. + */ + if (!prog->call_printk) + return 0; + + for (i = 0; i < ARRAY_SIZE(denylist); i++) { + if (!strcmp(denylist[i], name)) + return 1; + } + return 0; +} + +static int check_tp_printk_denylist(struct bpf_verifier_env *env, int func_id) +{ + struct bpf_prog *prog = env->prog; + + if (prog->type != BPF_PROG_TYPE_TRACING || + prog->expected_attach_type != BPF_TRACE_RAW_TP) + return 0; + + if (WARN_ON_ONCE(!prog->aux->attach_func_name)) + return -EINVAL; + + if (!bpf_check_tp_printk_denylist(prog->aux->attach_func_name, prog)) + return 0; + + verbose(env, "Can't attach program with %s#%d helper to %s tracepoint.\n", + func_id_name(func_id), func_id, prog->aux->attach_func_name); + return -EACCES; +} + static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn, int *insn_idx_p) { @@ -7675,6 +7716,11 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn err = __check_func_call(env, insn, insn_idx_p, meta.subprogno, set_user_ringbuf_callback_state); break; + case BPF_FUNC_trace_printk: + case BPF_FUNC_trace_vprintk: + env->prog->call_printk = 1; + err = check_tp_printk_denylist(env, func_id); + break; } if (err) -- 2.38.1
