bpf: Mark direct ld of stashed bpf_{rb,list}_node as non-owning ref
This patch enables the following pattern: /* mapval contains a __kptr pointing to refcounted local kptr */ mapval = bpf_map_lookup_elem(&map, &idx); if (!mapval || !mapval->some_kptr) { /* omitted */ } p = bpf_refcount_acquire(&mapval->some_kptr); Currently this doesn't work because bpf_refcount_acquire expects an owning or non-owning ref. The verifier defines non-owning ref as a type: PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF while mapval->some_kptr is PTR_TO_BTF_ID | PTR_UNTRUSTED. It's possible to do the refcount_acquire by first bpf_kptr_xchg'ing mapval->some_kptr into a temp kptr, refcount_acquiring that, and xchg'ing back into mapval, but this is unwieldy and shouldn't be necessary. This patch modifies btf_ld_kptr_type such that user-allocated types are marked MEM_ALLOC and if those types have a bpf_{rb,list}_node they're marked NON_OWN_REF as well. Additionally, due to changes to bpf_obj_drop_impl earlier in this series, rcu_protected_object now returns true for all user-allocated types, resulting in mapval->some_kptr being marked MEM_RCU. After this patch's changes, mapval->some_kptr is now: PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU which results in it passing the non-owning ref test, and the motivating example passing verification. Future work will likely get rid of special non-owning ref lifetime logic in the verifier, at which point we'll be able to delete the NON_OWN_REF flag entirely. Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> Link: https://lore.kernel.org/r/20231107085639.3016113-6-davemarchevsky@fb.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>
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