RE: [PATCH bpf-next 1/3] bpf: decouple prune and jump points

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> BPF verifier marks some instructions as prune points. Currently these
> prune points serve two purposes.
> 
> It's a point where verifier tries to find previously verified state and
> check current state's equivalence to short circuit verification for
> current code path.
> 
> But also currently it's a point where jump history, used for precision
> backtracking, is updated. This is done so that non-linear flow of
> execution could be properly backtracked.
> 
> Such coupling is coincidental and unnecessary. Some prune points are not
> part of some non-linear jump path, so don't need update of jump history.
> On the other hand, not all instructions which have to be recorded in
> jump history necessarily are good prune points.
> 
> This patch splits prune and jump points into independent flags.
> Currently all prune points are marked as jump points to minimize amount
> of changes in this patch, but next patch will perform some optimization
> of prune vs jmp point placement.
> 
> No functional changes are intended.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: John Fastabend <john.fastabend@gmail.com>

> ---
>  include/linux/bpf_verifier.h |  1 +
>  kernel/bpf/verifier.c        | 57 +++++++++++++++++++++++++++---------
>  2 files changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index b5090e89cb3f..9870d1d0df01 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -452,6 +452,7 @@ struct bpf_insn_aux_data {
>  	/* below fields are initialized once */
>  	unsigned int orig_idx; /* original instruction index */
>  	bool prune_point;
> +	bool jmp_point;

Random thought we might want to make these flags in the future so you
can have,

   type = BPF_PRUNE_POINT | BPF_JMP_POINT | BPF_ITERATOR_POINT

and so on without a bunch of bools.

>  };
>