bpf: introduce bpf_perf_event_output() helper

This helper is used to send raw data from eBPF program into
special PERF_TYPE_SOFTWARE/PERF_COUNT_SW_BPF_OUTPUT perf_event.
User space needs to perf_event_open() it (either for one or all cpus) and
store FD into perf_event_array (similar to bpf_perf_event_read() helper)
before eBPF program can send data into it.

Today the programs triggered by kprobe collect the data and either store
it into the maps or print it via bpf_trace_printk() where latter is the debug
facility and not suitable to stream the data. This new helper replaces
such bpf_trace_printk() usage and allows programs to have dedicated
channel into user space for post-processing of the raw data collected.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 62 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 564f1f091991..2e032426cfb7 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -287,6 +287,17 @@ enum bpf_func_id {
          * Return: realm if != 0
          */
         BPF_FUNC_get_route_realm,
+
+        /**
+         * bpf_perf_event_output(ctx, map, index, data, size) - output perf raw sample
+         * @ctx: struct pt_regs*
+         * @map: pointer to perf_event_array map
+         * @index: index of event in the map
+         * @data: data on stack to be output as raw data
+         * @size: size of data
+         * Return: 0 on success
+         */
+        BPF_FUNC_perf_event_output,
         __BPF_FUNC_MAX_ID,
 };
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 2881145cda86..d3c417615361 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -110,6 +110,7 @@ enum perf_sw_ids {
         PERF_COUNT_SW_ALIGNMENT_FAULTS          = 7,
         PERF_COUNT_SW_EMULATION_FAULTS          = 8,
         PERF_COUNT_SW_DUMMY                     = 9,
+        PERF_COUNT_SW_BPF_OUTPUT                = 10,
 
         PERF_COUNT_SW_MAX,                      /* non-ABI */
 };
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index f2d9e698c753..e3cfe46b074f 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -295,6 +295,8 @@ static void *perf_event_fd_array_get_ptr(struct bpf_map *map, int fd)
                 return (void *)attr;
 
         if (attr->type != PERF_TYPE_RAW &&
+            !(attr->type == PERF_TYPE_SOFTWARE &&
+              attr->config == PERF_COUNT_SW_BPF_OUTPUT) &&
             attr->type != PERF_TYPE_HARDWARE) {
                 perf_event_release_kernel(event);
                 return ERR_PTR(-EINVAL);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1d6b97be79e1..b56cf51f8d42 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -245,6 +245,7 @@ static const struct {
 } func_limit[] = {
         {BPF_MAP_TYPE_PROG_ARRAY, BPF_FUNC_tail_call},
         {BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_read},
+        {BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_output},
 };
 
 static void print_verifier_state(struct verifier_env *env)
@@ -910,7 +911,7 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
                  * don't allow any other map type to be passed into
                  * the special func;
                  */
-                if (bool_map != bool_func)
+                if (bool_func && bool_map != bool_func)
                         return -EINVAL;
         }
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0fe96c7c8803..47febbe7998e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -215,6 +215,50 @@ const struct bpf_func_proto bpf_perf_event_read_proto = {
         .arg2_type      = ARG_ANYTHING,
 };
 
+static u64 bpf_perf_event_output(u64 r1, u64 r2, u64 index, u64 r4, u64 size)
+{
+        struct pt_regs *regs = (struct pt_regs *) (long) r1;
+        struct bpf_map *map = (struct bpf_map *) (long) r2;
+        struct bpf_array *array = container_of(map, struct bpf_array, map);
+        void *data = (void *) (long) r4;
+        struct perf_sample_data sample_data;
+        struct perf_event *event;
+        struct perf_raw_record raw = {
+                .size = size,
+                .data = data,
+        };
+
+        if (unlikely(index >= array->map.max_entries))
+                return -E2BIG;
+
+        event = (struct perf_event *)array->ptrs[index];
+        if (unlikely(!event))
+                return -ENOENT;
+
+        if (unlikely(event->attr.type != PERF_TYPE_SOFTWARE ||
+                     event->attr.config != PERF_COUNT_SW_BPF_OUTPUT))
+                return -EINVAL;
+
+        if (unlikely(event->oncpu != smp_processor_id()))
+                return -EOPNOTSUPP;
+
+        perf_sample_data_init(&sample_data, 0, 0);
+        sample_data.raw = &raw;
+        perf_event_output(event, &sample_data, regs);
+        return 0;
+}
+
+static const struct bpf_func_proto bpf_perf_event_output_proto = {
+        .func           = bpf_perf_event_output,
+        .gpl_only       = false,
+        .ret_type       = RET_INTEGER,
+        .arg1_type      = ARG_PTR_TO_CTX,
+        .arg2_type      = ARG_CONST_MAP_PTR,
+        .arg3_type      = ARG_ANYTHING,
+        .arg4_type      = ARG_PTR_TO_STACK,
+        .arg5_type      = ARG_CONST_STACK_SIZE,
+};
+
 static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
 {
         switch (func_id) {
@@ -242,6 +286,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
                 return &bpf_get_smp_processor_id_proto;
         case BPF_FUNC_perf_event_read:
                 return &bpf_perf_event_read_proto;
+        case BPF_FUNC_perf_event_output:
+                return &bpf_perf_event_output_proto;
         default:
                 return NULL;
         }