On 9/10/24 8:37 PM, Philo Lu wrote:
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@xxxxxxxxxx>
Signed-off-by: Philo Lu <lulie@xxxxxxxxxxxxxxxxx>
---
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,
The "prog" arg is not used, so the following nit...
+ 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]))
... I changed it to directly use
btf_param_match_suffix(btf, &args[arg], "__nullable"),
and removed the new prog_arg_maybe_null(). There are already a few
is_kfunc_arg_{nullable, ...} helpers in verifier.c. Maybe we can consider
refactoring them (if) there are more use cases like this in the future.
