On Mon, Feb 27, 2023 at 08:01:18PM -0800, Alexei Starovoitov wrote: > From: Alexei Starovoitov <ast@xxxxxxxxxx> > > bpf programs sometimes do: > bpf_cgrp_storage_get(&map, task->cgroups->dfl_cgrp, ...); > It is safe to do, because cgroups->dfl_cgrp pointer is set diring init and > never changes. The task->cgroups is also never NULL. It is also set during init > and will change when task switches cgroups. For any trusted task pointer > dereference of cgroups and dfl_cgrp should yield trusted pointers. The verifier > wasn't aware of this. Hence in gcc compiled kernels task->cgroups dereference > was producing PTR_TO_BTF_ID without modifiers while in clang compiled kernels > the verifier recognizes __rcu tag in cgroups field and produces > PTR_TO_BTF_ID | MEM_RCU | MAYBE_NULL. > Tag cgroups and dfl_cgrp as trusted to equalize clang and gcc behavior. > When GCC supports btf_type_tag such tagging will done directly in the type. > > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Acked-by: David Vernet <void@xxxxxxxxxxxxx>
