From fb8d353bb58f4928337591ef2c49820fb71faff2 Mon Sep 17 00:00:00 2001 From: Amery Hung Date: Fri, 11 Sep 2026 15:04:04 -0700 Subject: bpf: Resolve BTF ID of ARG_PTR_TO_BTF_ID in kfunc bpf_func_proto check_kfunc_args() walks the kfunc's BTF on every verification of a call to work out which BTF ID an ARG_PTR_TO_BTF_ID argument expects. Helpers name theirs in bpf_func_proto::arg_btf_id[], as a pointer to a BTF ID that resolve_btfids fills in at build time. The ID of a kfunc argument's referent is already stored in the immutable BTF records that describe its pointer and modifier chain. Make arg_btf_id[] point to the BTF field containing the resolved ID. A __map argument instead uses the existing vmlinux BTF ID pointer. Produce this metadata alongside the argument classification in get_kfunc_arg_type(). Declare the argument BTF ID pointers const, since the verifier only reads through them. The BTF object owns their storage and remains alive while the generated prototype is used, so the pointers remain valid when the kfunc descriptor array is reallocated or sorted. Both helper and kfunc callers can now read the expected BTF ID through the same bpf_func_proto field, which lets check_func_arg() take over the ARG_PTR_TO_BTF_ID case. arg_btf_id[] shares a union with arg_size[], so an argument cannot store both. The scalar-struct memory fallback keeps resolving its byte size at verification time, as it does today. No functional change. Signed-off-by: Amery Hung Link: https://lore.kernel.org/r/20260911220415.1396439-13-ameryhung@gmail.com Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index aa4d3bb5e8cc..d0066d744ceb 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1021,13 +1021,13 @@ struct bpf_func_proto { }; union { struct { - u32 *arg1_btf_id; - u32 *arg2_btf_id; - u32 *arg3_btf_id; - u32 *arg4_btf_id; - u32 *arg5_btf_id; + const u32 *arg1_btf_id; + const u32 *arg2_btf_id; + const u32 *arg3_btf_id; + const u32 *arg4_btf_id; + const u32 *arg5_btf_id; }; - u32 *arg_btf_id[MAX_BPF_FUNC_ARGS]; + const u32 *arg_btf_id[MAX_BPF_FUNC_ARGS]; struct { size_t arg1_size; size_t arg2_size; -- cgit v1.2.3