On Sun, Sep 04, 2022 at 10:41:28PM +0200, Kumar Kartikeya Dwivedi wrote:
> For a lot of use cases in future patches, we will want to modify the
> state of registers part of some same 'group' (e.g. same ref_obj_id). It
> won't just be limited to releasing reference state, but setting a type
> flag dynamically based on certain actions, etc.
>
> Hence, we need a way to easily pass a callback to the function that
> iterates over all registers in current bpf_verifier_state in all frames
> upto (and including) the curframe.
>
> While in C++ we would be able to easily use a lambda to pass state and
> the callback together, sadly we aren't using C++ in the kernel. The next
> best thing to avoid defining a function for each case seems like
> statement expressions in GNU C. The kernel already uses them heavily,
> hence they can passed to the macro in the style of a lambda. The
> statement expression will then be substituted in the for loop bodies.
>
> Variables __state and __reg are set to current bpf_func_state and reg
> for each invocation of the expression inside the passed in verifier
> state.
>
> Then, convert mark_ptr_or_null_regs, clear_all_pkt_pointers,
> release_reference, find_good_pkt_pointers, find_equal_scalars to
> use bpf_expr_for_each_reg_in_vstate.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> include/linux/bpf_verifier.h | 21 ++++++
> kernel/bpf/verifier.c | 135 ++++++++---------------------------
> 2 files changed, 49 insertions(+), 107 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index c6d550978d63..73d9443d0074 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -354,6 +354,27 @@ struct bpf_verifier_state {
> iter < frame->allocated_stack / BPF_REG_SIZE; \
> iter++, reg = bpf_get_spilled_reg(iter, frame))
>
> +/* Invoke __expr over regsiters in __vst, setting __state and __reg */
> +#define bpf_expr_for_each_reg_in_vstate(__vst, __state, __reg, __expr) \
Very nice.
I renamed it to bpf_for_each_reg_in_vstate to make it less verbose
and more consistent with existing bpf_for_each_spilled_reg.
And applied to bpf-next.
