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Date:   Thu, 30 May 2019 15:55:48 -0700
From:   Matt Mullins <mmullins@...com>
To:     <hall@...com>, <mmullins@...com>, <ast@...nel.org>,
        <bpf@...r.kernel.org>, <netdev@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, "Yonghong Song" <yhs@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH bpf] bpf: preallocate a perf_sample_data per event fd

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@...com>
---
It felt a bit overkill, but I had to split bpf_event_entry into its own
header file to break an include cycle from perf_event.h -> cgroup.h ->
cgroup-defs.h -> bpf-cgroup.h -> bpf.h -> (potentially) perf_event.h.

 include/linux/bpf.h       |  7 -------
 include/linux/bpf_event.h | 20 ++++++++++++++++++++
 kernel/bpf/arraymap.c     |  2 ++
 kernel/trace/bpf_trace.c  | 30 +++++++++++++++++-------------
 4 files changed, 39 insertions(+), 20 deletions(-)
 create mode 100644 include/linux/bpf_event.h

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4fb3aa2dc975..13b253a36402 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -467,13 +467,6 @@ static inline bool bpf_map_flags_access_ok(u32 access_flags)
 	       (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG);
 }
 
-struct bpf_event_entry {
-	struct perf_event *event;
-	struct file *perf_file;
-	struct file *map_file;
-	struct rcu_head rcu;
-};
-
 bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *fp);
 int bpf_prog_calc_tag(struct bpf_prog *fp);
 
diff --git a/include/linux/bpf_event.h b/include/linux/bpf_event.h
new file mode 100644
index 000000000000..9f415990f921
--- /dev/null
+++ b/include/linux/bpf_event.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BPF_EVENT_H
+#define _LINUX_BPF_EVENT_H
+
+#include <linux/perf_event.h>
+#include <linux/types.h>
+
+struct file;
+
+struct bpf_event_entry {
+	struct perf_event *event;
+	struct file *perf_file;
+	struct file *map_file;
+	struct rcu_head rcu;
+	struct perf_sample_data sd;
+	atomic_t in_use;
+};
+
+#endif /* _LINUX_BPF_EVENT_H */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 584636c9e2eb..08e5e486d563 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -11,6 +11,7 @@
  * General Public License for more details.
  */
 #include <linux/bpf.h>
+#include <linux/bpf_event.h>
 #include <linux/btf.h>
 #include <linux/err.h>
 #include <linux/slab.h>
@@ -659,6 +660,7 @@ static struct bpf_event_entry *bpf_event_entry_gen(struct file *perf_file,
 		ee->event = perf_file->private_data;
 		ee->perf_file = perf_file;
 		ee->map_file = map_file;
+		atomic_set(&ee->in_use, 0);
 	}
 
 	return ee;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f92d6ad5e080..a03e29957698 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -6,6 +6,7 @@
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/bpf.h>
+#include <linux/bpf_event.h>
 #include <linux/bpf_perf_event.h>
 #include <linux/filter.h>
 #include <linux/uaccess.h>
@@ -410,17 +411,17 @@ 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 +440,22 @@ __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);
+	if (atomic_cmpxchg(&ee->in_use, 0, 1) != 0)
+		return -EBUSY;
+
+	sd = &ee->sd;
+	perf_sample_data_init(sd, 0, 0);
+	sd->raw = raw;
+
+	ret = perf_event_output(event, sd, regs);
+
+	atomic_set(&ee->in_use, 0);
+	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 +466,8 @@ 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 +482,10 @@ 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 +503,8 @@ 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

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