On Wed, Oct 7, 2026 at 9:25 AM Yiyang Chen <[email protected]> wrote: > > A global subprogram parameter tagged __arg_trusted is verified with > PTR_TRUSTED, but the common call-site type check accepts bare PTR_TO_BTF_ID > and MEM_RCU registers. The callee can consequently pass a pointer with > weaker provenance to a kfunc that does not accept RCU-protected pointers. > > RCU protection only guarantees that the object remains allocated through a > grace period. It does not guarantee that an object's refcount is nonzero, > so an RCU-protected pointer cannot satisfy the trusted-pointer contract. > For example, an RCU-protected bpf_cpumask loaded from a map may have a > zero refcount. Passing it through __arg_trusted lets the callee pass it > to bpf_cpumask_acquire(), whose plain refcount_inc() can retain an object > that will be freed after the grace period. > > Make the existing provenance check contract-driven. Mark generated BTF ID > kfunc argument types with PTR_TRUSTED, and add MEM_RCU only for KF_RCU > kfuncs. Normalize PTR_MAYBE_NULL when the argument contract permits it. > Then use the argument flags to require trusted or referenced provenance > and allow MEM_RCU only when the contract says so. > > Split is_trusted_reg() so the normalized type is used for type and modifier > checks while reference lookup still uses the original register. Conversion > of scalar-struct BTF ID arguments to fixed-size memory continues to > construct a new ARG_PTR_TO_MEM type without PTR_TRUSTED. > > Fixes: e2b3c4ff5d18 ("bpf: add __arg_trusted global func arg tag") > Suggested-by: Amery Hung <[email protected]> > Signed-off-by: Yiyang Chen <[email protected]> > --- > kernel/bpf/verifier.c | 27 ++++++++++++++++++++------- > 1 file changed, 20 insertions(+), 7 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 353bde9ae2274..a0ab793f041d8 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5327,15 +5327,17 @@ static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = { > [CONST_PTR_TO_MAP] = btf_bpf_map_id, > }; > > -static bool is_trusted_reg(struct bpf_verifier_env *env, const struct > bpf_reg_state *reg) > +static bool is_trusted_reg_type(struct bpf_verifier_env *env, > + const struct bpf_reg_state *reg, > + enum bpf_reg_type type)
You might want to teach your agent that the line limit is 100 columns. There are several unnecessary line wrapping. The fix looks good to me. Sashiko’s finding is real but pre-existing, so it does not need to block this patch. If you respin, consider fixing it in a separate patch with a PTR_UNTRUSTED | MEM_RCU KF_RCU regression test. Reviewed-by: Amery Hung <[email protected]>
