On Tue, 2026-01-20 at 16:28 +0800, Zesen Liu wrote: > 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 <[email protected]> > Signed-off-by: Shuran Liu <[email protected]> > Co-developed-by: Peili Gao <[email protected]> > Signed-off-by: Peili Gao <[email protected]> > Co-developed-by: Haoran Ni <[email protected]> > Signed-off-by: Haoran Ni <[email protected]> > Signed-off-by: Zesen Liu <[email protected]> > ---
At the moment, for helper arguments processing I see that MEM_RDONLY influences verifier only when argument type is ARG_PTR_TO_DYNPTR or ARG_PTR_TO_BTF_ID. Hence, I think this change is safe to apply, effects are limited to the check_mem_arg_rw_flag_ok() below. Reviewed-by: Eduard Zingerman <[email protected]> > 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; > } >
