Re: [PATCH bpf-next v5 5/8] bpf: teach the verifier to enforce css_iter and task_iter in RCU CS

[Andrii Nakryiko]

On Wed, Oct 11, 2023 at 5:09 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
>
> css_iter and task_iter should be used in rcu section. Specifically, in
> sleepable progs explicit bpf_rcu_read_lock() is needed before use these
> iters. In normal bpf progs that have implicit rcu_read_lock(), it's OK to
> use them directly.
>
> This patch adds a new a KF flag KF_RCU_PROTECTED for bpf_iter_task_new and
> bpf_iter_css_new. It means the kfunc should be used in RCU CS. We check
> whether we are in rcu cs before we want to invoke this kfunc. If the rcu
> protection is guaranteed, we would let st->type = PTR_TO_STACK | MEM_RCU.
> Once user do rcu_unlock during the iteration, state MEM_RCU of regs would
> be cleared. is_iter_reg_valid_init() will reject if reg->type is UNTRUSTED.
>
> It is worth noting that currently, bpf_rcu_read_unlock does not
> clear the state of the STACK_ITER reg, since bpf_for_each_spilled_reg
> only considers STACK_SPILL. This patch also let bpf_for_each_spilled_reg
> search STACK_ITER.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
> ---
>  include/linux/bpf_verifier.h | 19 ++++++++------
>  include/linux/btf.h          |  1 +
>  kernel/bpf/helpers.c         |  4 +--
>  kernel/bpf/verifier.c        | 50 ++++++++++++++++++++++++++++--------
>  4 files changed, 53 insertions(+), 21 deletions(-)
>

LGTM.

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>