On Mon, Dec 5, 2022 at 4:28 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > On Sat, Dec 03, 2022 at 09:58:34AM -0800, Namhyung Kim wrote: > > On Wed, Nov 30, 2022 at 03:29:39PM -0800, Andrii Nakryiko wrote: > > > On Fri, Nov 25, 2022 at 1:35 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > > > > > > > On Thu, Nov 24, 2022 at 09:17:22AM -0800, Alexei Starovoitov wrote: > > > > > On Thu, Nov 24, 2022 at 1:42 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > > > > > > > > > > > On Thu, Nov 24, 2022 at 01:41:23AM +0100, Daniel Borkmann wrote: > > > > > > > On 11/21/22 10:31 PM, Jiri Olsa wrote: > > > > > > > > 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. > > > > > > > > + */ > > > > > > > > > > > > > > What if that prog doesn't but tail calls into another one which calls printk helpers? > > > > > > > > > > > > right, I'll deny that for all BPF_PROG_TYPE_RAW_TRACEPOINT* programs, > > > > > > because I don't see easy way to check on that > > > > > > > > > > > > we can leave printk check for tracing BPF_TRACE_RAW_TP programs, > > > > > > because verifier known the exact tracepoint already > > > > > > > > > > This is all fragile and merely a stop gap. > > > > > Doesn't sound that the issue is limited to bpf_trace_printk > > > > > > > > hm, I don't have a better idea how to fix that.. I can't deny > > > > contention_begin completely, because we use it in perf via > > > > tp_btf/contention_begin (perf lock contention) and I don't > > > > think there's another way for perf to do that > > > > > > > > fwiw the last version below denies BPF_PROG_TYPE_RAW_TRACEPOINT > > > > programs completely and tracing BPF_TRACE_RAW_TP with printks > > > > > > > > > > I think disabling bpf_trace_printk() tracepoint for any BPF program is > > > totally fine. This tracepoint was never intended to be attached to. > > > > > > But as for the general bpf_trace_printk() deadlocking. Should we > > > discuss how to make it not deadlock instead of starting to denylist > > > things left and right? > > > > > > Do I understand that we take trace_printk_lock only to protect that > > > static char buf[]? Can we just make this buf per-CPU and do a trylock > > > instead? We'll only fail to bpf_trace_printk() something if we have > > > nested BPF programs (rare) or NMI (also rare). > > > > > > And it's a printk(), it's never mission-critical, so if we drop some > > > message in rare case it's totally fine. > > > > What about contention_begin? I wonder if we can disallow recursions > > for those in the deny list like using bpf_prog_active.. > > I was testing change below which allows to check recursion just > for contention_begin tracepoint > > for the reported issue we might be ok with the change that Andrii > suggested, but we could have the change below as extra precaution > > jirka > > > --- > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h > index 20749bd9db71..1c89d4292374 100644 > --- a/include/linux/trace_events.h > +++ b/include/linux/trace_events.h > @@ -740,8 +740,8 @@ unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx); > int perf_event_attach_bpf_prog(struct perf_event *event, struct bpf_prog *prog, u64 bpf_cookie); > void perf_event_detach_bpf_prog(struct perf_event *event); > int perf_event_query_prog_array(struct perf_event *event, void __user *info); > -int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog); > -int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog); > +int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_raw_event_data *data); > +int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_raw_event_data *data); > struct bpf_raw_event_map *bpf_get_raw_tracepoint(const char *name); > void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp); > int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id, > @@ -873,31 +873,31 @@ void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp); > int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog, u64 bpf_cookie); > void perf_event_free_bpf_prog(struct perf_event *event); > > -void bpf_trace_run1(struct bpf_prog *prog, u64 arg1); > -void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2); > -void bpf_trace_run3(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run1(struct bpf_raw_event_data *data, u64 arg1); > +void bpf_trace_run2(struct bpf_raw_event_data *data, u64 arg1, u64 arg2); > +void bpf_trace_run3(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3); > -void bpf_trace_run4(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run4(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4); > -void bpf_trace_run5(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run5(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5); > -void bpf_trace_run6(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run6(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6); > -void bpf_trace_run7(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run7(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7); > -void bpf_trace_run8(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run8(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7, > u64 arg8); > -void bpf_trace_run9(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run9(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7, > u64 arg8, u64 arg9); > -void bpf_trace_run10(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run10(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7, > u64 arg8, u64 arg9, u64 arg10); > -void bpf_trace_run11(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run11(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7, > u64 arg8, u64 arg9, u64 arg10, u64 arg11); > -void bpf_trace_run12(struct bpf_prog *prog, u64 arg1, u64 arg2, > +void bpf_trace_run12(struct bpf_raw_event_data *data, u64 arg1, u64 arg2, > u64 arg3, u64 arg4, u64 arg5, u64 arg6, u64 arg7, > u64 arg8, u64 arg9, u64 arg10, u64 arg11, u64 arg12); > void perf_trace_run_bpf_submit(void *raw_data, int size, int rctx, > diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h > index e7c2276be33e..5312a8b149c0 100644 > --- a/include/linux/tracepoint-defs.h > +++ b/include/linux/tracepoint-defs.h > @@ -46,6 +46,11 @@ typedef const int tracepoint_ptr_t; > typedef struct tracepoint * const tracepoint_ptr_t; > #endif > > +struct bpf_raw_event_data { > + struct bpf_prog *prog; > + int __percpu *recursion; > +}; > + > struct bpf_raw_event_map { > struct tracepoint *tp; > void *bpf_func; > diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h > index 6a13220d2d27..a8f9c3c7c447 100644 > --- a/include/trace/bpf_probe.h > +++ b/include/trace/bpf_probe.h > @@ -81,8 +81,8 @@ > static notrace void \ > __bpf_trace_##call(void *__data, proto) \ > { \ > - struct bpf_prog *prog = __data; \ > - CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(prog, CAST_TO_U64(args)); \ > + struct bpf_raw_event_data *____data = __data; \ > + CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(____data, CAST_TO_U64(args)); \ > } > > #undef DECLARE_EVENT_CLASS > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 35972afb6850..5dcb32cd24e6 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -3141,9 +3141,36 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, > return err; > } > > +static bool needs_recursion_check(struct bpf_raw_event_map *btp) > +{ > + return !strcmp(btp->tp->name, "contention_begin"); > +} > + > +static int bpf_raw_event_data_init(struct bpf_raw_event_data *data, > + struct bpf_raw_event_map *btp, > + struct bpf_prog *prog) > +{ > + int __percpu *recursion = NULL; > + > + if (needs_recursion_check(btp)) { > + recursion = alloc_percpu_gfp(int, GFP_KERNEL); > + if (!recursion) > + return -ENOMEM; > + } > + data->recursion = recursion; > + data->prog = prog; > + return 0; > +} > + > +static void bpf_raw_event_data_release(struct bpf_raw_event_data *data) > +{ > + free_percpu(data->recursion); > +} > + > struct bpf_raw_tp_link { > struct bpf_link link; > struct bpf_raw_event_map *btp; > + struct bpf_raw_event_data data; > }; > > static void bpf_raw_tp_link_release(struct bpf_link *link) > @@ -3151,7 +3178,8 @@ static void bpf_raw_tp_link_release(struct bpf_link *link) > struct bpf_raw_tp_link *raw_tp = > container_of(link, struct bpf_raw_tp_link, link); > > - bpf_probe_unregister(raw_tp->btp, raw_tp->link.prog); > + bpf_probe_unregister(raw_tp->btp, &raw_tp->data); > + bpf_raw_event_data_release(&raw_tp->data); > bpf_put_raw_tracepoint(raw_tp->btp); > } > > @@ -3338,17 +3366,23 @@ static int bpf_raw_tp_link_attach(struct bpf_prog *prog, > err = -ENOMEM; > goto out_put_btp; > } > + if (bpf_raw_event_data_init(&link->data, btp, prog)) { > + err = -ENOMEM; > + kfree(link); > + goto out_put_btp; > + } > bpf_link_init(&link->link, BPF_LINK_TYPE_RAW_TRACEPOINT, > &bpf_raw_tp_link_lops, prog); > link->btp = btp; > > err = bpf_link_prime(&link->link, &link_primer); > if (err) { > + bpf_raw_event_data_release(&link->data); > kfree(link); > goto out_put_btp; > } > > - err = bpf_probe_register(link->btp, prog); > + err = bpf_probe_register(link->btp, &link->data); > if (err) { > bpf_link_cleanup(&link_primer); > goto out_put_btp; > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 3bbd3f0c810c..d27b7dc77894 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2252,9 +2252,8 @@ void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp) > } > > static __always_inline > -void __bpf_trace_run(struct bpf_prog *prog, u64 *args) > +void __bpf_trace_prog_run(struct bpf_prog *prog, u64 *args) > { > - cant_sleep(); > if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) { > bpf_prog_inc_misses_counter(prog); > goto out; > @@ -2266,6 +2265,22 @@ void __bpf_trace_run(struct bpf_prog *prog, u64 *args) > this_cpu_dec(*(prog->active)); > } > > +static __always_inline > +void __bpf_trace_run(struct bpf_raw_event_data *data, u64 *args) > +{ > + struct bpf_prog *prog = data->prog; > + > + cant_sleep(); > + if (unlikely(!data->recursion)) > + return __bpf_trace_prog_run(prog, args); > + > + if (unlikely(this_cpu_inc_return(*(data->recursion)))) > + goto out; > + __bpf_trace_prog_run(prog, args); > +out: > + this_cpu_dec(*(data->recursion)); > +} This is way too much run-time and memory overhead to address this corner case. Pls come up with some other approach. Sorry I don't have decent suggestions at the moment. For now we can simply disallow attaching to contention_begin.
