[PATCH bpf-next v3 2/2] bpf: Require ARG_PTR_TO_MEM with memory flag

Zesen Liu
2026-01-20T08:29:47Z

Add check to ensure that ARG_PTR_TO_MEM is used with either MEM_WRITE or
MEM_RDONLY.

Using ARG_PTR_TO_MEM alone without flags does not make sense because:

- If the helper does not change the argument, missing MEM_RDONLY causes the
verifier to incorrectly reject a read-only buffer.
- If the helper does change the argument, missing MEM_WRITE causes the
verifier to incorrectly assume the memory is unchanged, leading to errors
in code optimization.

Co-developed-by: Shuran Liu <electronlsr@gmail.com>
Signed-off-by: Shuran Liu <electronlsr@gmail.com>
Co-developed-by: Peili Gao <gplhust955@gmail.com>
Signed-off-by: Peili Gao <gplhust955@gmail.com>
Co-developed-by: Haoran Ni <haoran.ni.cs@gmail.com>
Signed-off-by: Haoran Ni <haoran.ni.cs@gmail.com>
Signed-off-by: Zesen Liu <ftyghome@gmail.com>
---
kernel/bpf/verifier.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9de0ec0c3ed9..a89f5bc7eff7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10351,10 +10351,27 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
return true;
}

+static bool check_mem_arg_rw_flag_ok(const struct bpf_func_proto *fn)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
+ enum bpf_arg_type arg_type = fn->arg_type[i];
+
+ if (base_type(arg_type) != ARG_PTR_TO_MEM)
+ continue;
+ if (!(arg_type & (MEM_WRITE | MEM_RDONLY)))
+ return false;
+ }
+
+ return true;
+}
+
static int check_func_proto(const struct bpf_func_proto *fn)
{
return check_raw_mode_ok(fn) &&
check_arg_pair_ok(fn) &&
+ check_mem_arg_rw_flag_ok(fn) &&
check_btf_id_ok(fn) ? 0 : -EINVAL;
}

--
2.43.0