bpf: fix nested bpf tracepoints with per-cpu data

BPF_PROG_TYPE_RAW_TRACEPOINTs can be executed nested on the same CPU, as
they do not increment bpf_prog_active while executing.

This enables three levels of nesting, to support
  - a kprobe or raw tp or perf event,
  - another one of the above that irq context happens to call, and
  - another one in nmi context
(at most one of which may be a kprobe or perf event).

Fixes: 20b9d7ac4852 ("bpf: avoid excessive stack usage for perf_sample_data")
Signed-off-by: Matt Mullins <mmullins@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f92d6ad5e080671450b8eba785811718bddb1700..1c9a4745e596d91bde5fc5910fc4f8bcb318529e 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -410,8 +410,6 @@ static const struct bpf_func_proto bpf_perf_event_read_value_proto = {
        .arg4_type      = ARG_CONST_SIZE,
 };
 
-static DEFINE_PER_CPU(struct perf_sample_data, bpf_trace_sd);
-
 static __always_inline u64
 __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map,
                        u64 flags, struct perf_sample_data *sd)
@@ -442,24 +440,50 @@ __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map,
        return perf_event_output(event, sd, regs);
 }
 
+/*
+ * Support executing tracepoints in normal, irq, and nmi context that each call
+ * bpf_perf_event_output
+ */
+struct bpf_trace_sample_data {
+       struct perf_sample_data sds[3];
+};
+
+static DEFINE_PER_CPU(struct bpf_trace_sample_data, bpf_trace_sds);
+static DEFINE_PER_CPU(int, bpf_trace_nest_level);
 BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
           u64, flags, void *, data, u64, size)
 {
-       struct perf_sample_data *sd = this_cpu_ptr(&bpf_trace_sd);
+       struct bpf_trace_sample_data *sds = this_cpu_ptr(&bpf_trace_sds);
+       int nest_level = this_cpu_inc_return(bpf_trace_nest_level);
        struct perf_raw_record raw = {
                .frag = {
                        .size = size,
                        .data = data,
                },
        };
+       struct perf_sample_data *sd;
+       int err;
 
-       if (unlikely(flags & ~(BPF_F_INDEX_MASK)))
-               return -EINVAL;
+       if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(sds->sds))) {
+               err = -EBUSY;
+               goto out;
+       }
+
+       sd = &sds->sds[nest_level - 1];
+
+       if (unlikely(flags & ~(BPF_F_INDEX_MASK))) {
+               err = -EINVAL;
+               goto out;
+       }
 
        perf_sample_data_init(sd, 0, 0);
        sd->raw = &raw;
 
-       return __bpf_perf_event_output(regs, map, flags, sd);
+       err = __bpf_perf_event_output(regs, map, flags, sd);
+
+out:
+       this_cpu_dec(bpf_trace_nest_level);
+       return err;
 }
 
 static const struct bpf_func_proto bpf_perf_event_output_proto = {
@@ -822,16 +846,48 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 /*
  * bpf_raw_tp_regs are separate from bpf_pt_regs used from skb/xdp
  * to avoid potential recursive reuse issue when/if tracepoints are added
- * inside bpf_*_event_output, bpf_get_stackid and/or bpf_get_stack
+ * inside bpf_*_event_output, bpf_get_stackid and/or bpf_get_stack.
+ *
+ * Since raw tracepoints run despite bpf_prog_active, support concurrent usage
+ * in normal, irq, and nmi context.
  */
-static DEFINE_PER_CPU(struct pt_regs, bpf_raw_tp_regs);
+struct bpf_raw_tp_regs {
+       struct pt_regs regs[3];
+};
+static DEFINE_PER_CPU(struct bpf_raw_tp_regs, bpf_raw_tp_regs);
+static DEFINE_PER_CPU(int, bpf_raw_tp_nest_level);
+static struct pt_regs *get_bpf_raw_tp_regs(void)
+{
+       struct bpf_raw_tp_regs *tp_regs = this_cpu_ptr(&bpf_raw_tp_regs);
+       int nest_level = this_cpu_inc_return(bpf_raw_tp_nest_level);
+
+       if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(tp_regs->regs))) {
+               this_cpu_dec(bpf_raw_tp_nest_level);
+               return ERR_PTR(-EBUSY);
+       }
+
+       return &tp_regs->regs[nest_level - 1];
+}
+
+static void put_bpf_raw_tp_regs(void)
+{
+       this_cpu_dec(bpf_raw_tp_nest_level);
+}
+
 BPF_CALL_5(bpf_perf_event_output_raw_tp, struct bpf_raw_tracepoint_args *, args,
           struct bpf_map *, map, u64, flags, void *, data, u64, size)
 {
-       struct pt_regs *regs = this_cpu_ptr(&bpf_raw_tp_regs);
+       struct pt_regs *regs = get_bpf_raw_tp_regs();
+       int ret;
+
+       if (IS_ERR(regs))
+               return PTR_ERR(regs);
 
        perf_fetch_caller_regs(regs);
-       return ____bpf_perf_event_output(regs, map, flags, data, size);
+       ret = ____bpf_perf_event_output(regs, map, flags, data, size);
+
+       put_bpf_raw_tp_regs();
+       return ret;
 }
 
 static const struct bpf_func_proto bpf_perf_event_output_proto_raw_tp = {
@@ -848,12 +904,18 @@ static const struct bpf_func_proto bpf_perf_event_output_proto_raw_tp = {
 BPF_CALL_3(bpf_get_stackid_raw_tp, struct bpf_raw_tracepoint_args *, args,
           struct bpf_map *, map, u64, flags)
 {
-       struct pt_regs *regs = this_cpu_ptr(&bpf_raw_tp_regs);
+       struct pt_regs *regs = get_bpf_raw_tp_regs();
+       int ret;
+
+       if (IS_ERR(regs))
+               return PTR_ERR(regs);
 
        perf_fetch_caller_regs(regs);
        /* similar to bpf_perf_event_output_tp, but pt_regs fetched differently */
-       return bpf_get_stackid((unsigned long) regs, (unsigned long) map,
-                              flags, 0, 0);
+       ret = bpf_get_stackid((unsigned long) regs, (unsigned long) map,
+                             flags, 0, 0);
+       put_bpf_raw_tp_regs();
+       return ret;
 }
 
 static const struct bpf_func_proto bpf_get_stackid_proto_raw_tp = {
@@ -868,11 +930,17 @@ static const struct bpf_func_proto bpf_get_stackid_proto_raw_tp = {
 BPF_CALL_4(bpf_get_stack_raw_tp, struct bpf_raw_tracepoint_args *, args,
           void *, buf, u32, size, u64, flags)
 {
-       struct pt_regs *regs = this_cpu_ptr(&bpf_raw_tp_regs);
+       struct pt_regs *regs = get_bpf_raw_tp_regs();
+       int ret;
+
+       if (IS_ERR(regs))
+               return PTR_ERR(regs);
 
        perf_fetch_caller_regs(regs);
-       return bpf_get_stack((unsigned long) regs, (unsigned long) buf,
-                            (unsigned long) size, flags, 0);
+       ret = bpf_get_stack((unsigned long) regs, (unsigned long) buf,
+                           (unsigned long) size, flags, 0);
+       put_bpf_raw_tp_regs();
+       return ret;
 }
 
 static const struct bpf_func_proto bpf_get_stack_proto_raw_tp = {