Pointers passed to tp_btf were trusted to be valid, but some tracepoints
do take NULL pointer as input, such as trace_tcp_send_reset(). Then the
invalid memory access cannot be detected by verifier.

This patch fix it by add a suffix "__nullable" to the unreliable
argument. The suffix is shown in btf, and PTR_MAYBE_NULL will be added
to nullable arguments. Then users must check the pointer before use it.

A problem here is that we use "btf_trace_##call" to search func_proto.
As it is a typedef, argument names as well as the suffix are not
recorded. To solve this, I use bpf_raw_event_map to find
"__bpf_trace##template" from "btf_trace_##call", and then we can see the
suffix.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
---
  kernel/bpf/btf.c      |  9 +++++++++
  kernel/bpf/verifier.c | 36 ++++++++++++++++++++++++++++++++----
  2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1e29281653c62..d1ea38d08f301 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c

@@ -6385,6 +6385,12 @@ static bool prog_args_trusted(const struct bpf_prog *prog)
  	}
  }
  
+static bool prog_arg_maybe_null(const struct bpf_prog *prog, const struct btf *btf,

+				const struct btf_param *arg)
+{
+	return btf_param_match_suffix(btf, arg, "__nullable");
+}
+
  int btf_ctx_arg_offset(const struct btf *btf, const struct btf_type *func_proto,
  		       u32 arg_no)
  {

@@ -6554,6 +6560,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
  	if (prog_args_trusted(prog))
  		info->reg_type |= PTR_TRUSTED;
  
+	if (prog_arg_maybe_null(prog, btf, &args[arg]))