On Thu, Nov 3, 2022 at 8:21 AM Yonghong Song <yhs@xxxxxx> wrote:
>
> Currently, without rcu attribute info in BTF, the verifier treats
> rcu tagged pointer as a normal pointer. This might be a problem
> for sleepable program where rcu_read_lock()/unlock() is not available.
> For example, for a sleepable fentry program, if rcu protected memory
> access is interleaved with a sleepable helper/kfunc, it is possible
> the memory access after the sleepable helper/kfunc might be invalid
> since the object might have been freed then. To prevent such cases,
> introducing rcu tagging for memory accesses in verifier can help
> to reject such programs.
>
> To enable rcu tagging in BTF, during kernel compilation,
> define __rcu as attribute btf_type_tag("rcu") so __rcu information can
> be preserved in dwarf and btf, and later can be used for bpf prog verification.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
Acked-by: KP Singh <kpsingh@xxxxxxxxxx>
