Re: [bpf-next PATCH v5 2/5] bpf: extend bpf_base_func_proto helpers with probe_* and *current_task*

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On 5/24/20 6:50 PM, John Fastabend wrote:
Often it is useful when applying policy to know something about the
task. If the administrator has CAP_SYS_ADMIN rights then they can
use kprobe + networking hook and link the two programs together to
accomplish this. However, this is a bit clunky and also means we have
to call both the network program and kprobe program when we could just
use a single program and avoid passing metadata through sk_msg/skb->cb,
socket, maps, etc.

To accomplish this add probe_* helpers to bpf_base_func_proto programs
guarded by a perfmon_capable() check. New supported helpers are the
following,

  BPF_FUNC_get_current_task
  BPF_FUNC_current_task_under_cgroup

Nit: Stale commit message?

  BPF_FUNC_probe_read_user
  BPF_FUNC_probe_read_kernel
  BPF_FUNC_probe_read_user_str
  BPF_FUNC_probe_read_kernel_str

Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
---
  kernel/bpf/helpers.c     |   24 ++++++++++++++++++++++++
  kernel/trace/bpf_trace.c |   10 +++++-----
  2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 886949f..bb4fb63 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -601,6 +601,12 @@ const struct bpf_func_proto bpf_event_output_data_proto =  {
  	.arg5_type      = ARG_CONST_SIZE_OR_ZERO,
  };
+const struct bpf_func_proto bpf_get_current_task_proto __weak;
+const struct bpf_func_proto bpf_probe_read_user_proto __weak;
+const struct bpf_func_proto bpf_probe_read_user_str_proto __weak;
+const struct bpf_func_proto bpf_probe_read_kernel_proto __weak;
+const struct bpf_func_proto bpf_probe_read_kernel_str_proto __weak;
+
  const struct bpf_func_proto *
  bpf_base_func_proto(enum bpf_func_id func_id)
  {
@@ -648,6 +654,24 @@ bpf_base_func_proto(enum bpf_func_id func_id)
  	case BPF_FUNC_jiffies64:
  		return &bpf_jiffies64_proto;
  	default:
+		break;
+	}
+
+	if (!perfmon_capable())
+		return NULL;
+
+	switch (func_id) {
+	case BPF_FUNC_get_current_task:
+		return &bpf_get_current_task_proto;
+	case BPF_FUNC_probe_read_user:
+		return &bpf_probe_read_user_proto;
+	case BPF_FUNC_probe_read_kernel:
+		return &bpf_probe_read_kernel_proto;
+	case BPF_FUNC_probe_read_user_str:
+		return &bpf_probe_read_user_str_proto;
+	case BPF_FUNC_probe_read_kernel_str:
+		return &bpf_probe_read_kernel_str_proto;
+	default:
  		return NULL;
  	}
  }
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 9531f54..187cd69 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -147,7 +147,7 @@ BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size,
  	return ret;
  }
-static const struct bpf_func_proto bpf_probe_read_user_proto = {
+const struct bpf_func_proto bpf_probe_read_user_proto = {
  	.func		= bpf_probe_read_user,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,
@@ -167,7 +167,7 @@ BPF_CALL_3(bpf_probe_read_user_str, void *, dst, u32, size,
  	return ret;
  }
-static const struct bpf_func_proto bpf_probe_read_user_str_proto = {
+const struct bpf_func_proto bpf_probe_read_user_str_proto = {
  	.func		= bpf_probe_read_user_str,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,
@@ -198,7 +198,7 @@ BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
  	return bpf_probe_read_kernel_common(dst, size, unsafe_ptr, false);
  }
-static const struct bpf_func_proto bpf_probe_read_kernel_proto = {
+const struct bpf_func_proto bpf_probe_read_kernel_proto = {
  	.func		= bpf_probe_read_kernel,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,
@@ -253,7 +253,7 @@ BPF_CALL_3(bpf_probe_read_kernel_str, void *, dst, u32, size,
  	return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr, false);
  }
-static const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
+const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
  	.func		= bpf_probe_read_kernel_str,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,
@@ -907,7 +907,7 @@ BPF_CALL_0(bpf_get_current_task)
  	return (long) current;
  }
-static const struct bpf_func_proto bpf_get_current_task_proto = {
+const struct bpf_func_proto bpf_get_current_task_proto = {
  	.func		= bpf_get_current_task,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,





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