It is possible that a BPF program can be called while another BPF program is executing bpf_perf_event_output. This has been observed with I/O completion occurring as a result of an interrupt: bpf_prog_247fd1341cddaea4_trace_req_end+0x8d7/0x1000 ? trace_call_bpf+0x82/0x100 ? sch_direct_xmit+0xe2/0x230 ? blk_mq_end_request+0x1/0x100 ? blk_mq_end_request+0x5/0x100 ? kprobe_perf_func+0x19b/0x240 ? __qdisc_run+0x86/0x520 ? blk_mq_end_request+0x1/0x100 ? blk_mq_end_request+0x5/0x100 ? kprobe_ftrace_handler+0x90/0xf0 ? ftrace_ops_assist_func+0x6e/0xe0 ? ip6_input_finish+0xbf/0x460 ? 0xffffffffa01e80bf ? nbd_dbg_flags_show+0xc0/0xc0 [nbd] ? blkdev_issue_zeroout+0x200/0x200 ? blk_mq_end_request+0x1/0x100 ? blk_mq_end_request+0x5/0x100 ? flush_smp_call_function_queue+0x6c/0xe0 ? smp_call_function_single_interrupt+0x32/0xc0 ? call_function_single_interrupt+0xf/0x20 ? call_function_single_interrupt+0xa/0x20 ? swiotlb_map_page+0x140/0x140 ? refcount_sub_and_test+0x1a/0x50 ? tcp_wfree+0x20/0xf0 ? skb_release_head_state+0x62/0xc0 ? skb_release_all+0xe/0x30 ? napi_consume_skb+0xb5/0x100 ? mlx5e_poll_tx_cq+0x1df/0x4e0 ? mlx5e_poll_tx_cq+0x38c/0x4e0 ? mlx5e_napi_poll+0x58/0xc30 ? mlx5e_napi_poll+0x232/0xc30 ? net_rx_action+0x128/0x340 ? __do_softirq+0xd4/0x2ad ? irq_exit+0xa5/0xb0 ? do_IRQ+0x7d/0xc0 ? common_interrupt+0xf/0xf </IRQ> ? __rb_free_aux+0xf0/0xf0 ? perf_output_sample+0x28/0x7b0 ? perf_prepare_sample+0x54/0x4a0 ? perf_event_output+0x43/0x60 ? bpf_perf_event_output_raw_tp+0x15f/0x180 ? blk_mq_start_request+0x1/0x120 ? bpf_prog_411a64a706fc6044_should_trace+0xad4/0x1000 ? bpf_trace_run3+0x2c/0x80 ? nbd_send_cmd+0x4c2/0x690 [nbd] This also cannot be alleviated by further splitting the per-cpu perf_sample_data structs (as in commit 283ca526a9bd ("bpf: fix corruption on concurrent perf_event_output calls")), as a raw_tp could be attached to the block:block_rq_complete tracepoint and execute during another raw_tp. Instead, keep a pre-allocated perf_sample_data structure per perf_event_array element and fail a bpf_perf_event_output if that element is concurrently being used. Fixes: 20b9d7ac4852 ("bpf: avoid excessive stack usage for perf_sample_data") Signed-off-by: Matt Mullins <mmullins@xxxxxx> --- v1->v2: keep a pointer to the struct perf_sample_data rather than directly embedding it in the structure, avoiding the circular include and removing the need for in_use. Suggested by Song. include/linux/bpf.h | 1 + kernel/bpf/arraymap.c | 3 ++- kernel/trace/bpf_trace.c | 29 ++++++++++++++++------------- 3 files changed, 19 insertions(+), 14 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 4fb3aa2dc975..47fd85cfbbaf 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -472,6 +472,7 @@ struct bpf_event_entry { struct file *perf_file; struct file *map_file; struct rcu_head rcu; + struct perf_sample_data *sd; }; bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *fp); diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index 584636c9e2eb..c7f5d593e04f 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -654,11 +654,12 @@ static struct bpf_event_entry *bpf_event_entry_gen(struct file *perf_file, { struct bpf_event_entry *ee; - ee = kzalloc(sizeof(*ee), GFP_ATOMIC); + ee = kzalloc(sizeof(*ee) + sizeof(struct perf_sample_data), GFP_ATOMIC); if (ee) { ee->event = perf_file->private_data; ee->perf_file = perf_file; ee->map_file = map_file; + ee->sd = (void *)ee + sizeof(*ee); } return ee; diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index f92d6ad5e080..076f8e987355 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -410,17 +410,17 @@ 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) + u64 flags, struct perf_raw_record *raw) { struct bpf_array *array = container_of(map, struct bpf_array, map); unsigned int cpu = smp_processor_id(); u64 index = flags & BPF_F_INDEX_MASK; struct bpf_event_entry *ee; struct perf_event *event; + struct perf_sample_data *sd; + u64 ret; if (index == BPF_F_CURRENT_CPU) index = cpu; @@ -439,13 +439,22 @@ __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map, if (unlikely(event->oncpu != cpu)) return -EOPNOTSUPP; - return perf_event_output(event, sd, regs); + sd = xchg(&ee->sd, NULL); + if (!sd) + return -EBUSY; + + perf_sample_data_init(sd, 0, 0); + sd->raw = raw; + + ret = perf_event_output(event, sd, regs); + + xchg(&ee->sd, sd); + return ret; } 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 perf_raw_record raw = { .frag = { .size = size, @@ -456,10 +465,8 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map, if (unlikely(flags & ~(BPF_F_INDEX_MASK))) return -EINVAL; - perf_sample_data_init(sd, 0, 0); - sd->raw = &raw; - return __bpf_perf_event_output(regs, map, flags, sd); + return __bpf_perf_event_output(regs, map, flags, &raw); } static const struct bpf_func_proto bpf_perf_event_output_proto = { @@ -474,12 +481,10 @@ static const struct bpf_func_proto bpf_perf_event_output_proto = { }; static DEFINE_PER_CPU(struct pt_regs, bpf_pt_regs); -static DEFINE_PER_CPU(struct perf_sample_data, bpf_misc_sd); u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy) { - struct perf_sample_data *sd = this_cpu_ptr(&bpf_misc_sd); struct pt_regs *regs = this_cpu_ptr(&bpf_pt_regs); struct perf_raw_frag frag = { .copy = ctx_copy, @@ -497,10 +502,8 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, }; perf_fetch_caller_regs(regs); - perf_sample_data_init(sd, 0, 0); - sd->raw = &raw; - return __bpf_perf_event_output(regs, map, flags, sd); + return __bpf_perf_event_output(regs, map, flags, &raw); } BPF_CALL_0(bpf_get_current_task) -- 2.17.1