bpf: introduce bpf_get_current_task() helper

over time there were multiple requests to access different data
structures and fields of task_struct current, so finally add
the helper to access 'current' as-is. Tracing bpf programs will do
the rest of walking the pointers via bpf_probe_read().
Note that current can be null and bpf program has to deal it with,
but even dumb passing null into bpf_probe_read() is still safe.

Suggested-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c14ca1c..262a7e8 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -357,6 +357,13 @@ enum bpf_func_id {
         */
        BPF_FUNC_get_hash_recalc,
 
+       /**
+        * u64 bpf_get_current_task(void)
+        * Returns current task_struct
+        * Return: current
+        */
+       BPF_FUNC_get_current_task,
+
        __BPF_FUNC_MAX_ID,
 };
 

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 19c5b4a..094c716 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -312,6 +312,17 @@ const struct bpf_func_proto *bpf_get_event_output_proto(void)
        return &bpf_event_output_proto;
 }
 
+static u64 bpf_get_current_task(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+       return (long) current;
+}
+
+static const struct bpf_func_proto bpf_get_current_task_proto = {
+       .func           = bpf_get_current_task,
+       .gpl_only       = true,
+       .ret_type       = RET_INTEGER,
+};
+
 static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
 {
        switch (func_id) {
@@ -329,6 +340,8 @@ static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
                return &bpf_tail_call_proto;
        case BPF_FUNC_get_current_pid_tgid:
                return &bpf_get_current_pid_tgid_proto;
+       case BPF_FUNC_get_current_task:
+               return &bpf_get_current_task_proto;
        case BPF_FUNC_get_current_uid_gid:
                return &bpf_get_current_uid_gid_proto;
        case BPF_FUNC_get_current_comm: