netdev - Re: [PATCH v2 bpf-next 0/3] bpf/verifier: subprog/func

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Date:   Thu, 29 Mar 2018 23:50:05 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 0/3] bpf/verifier: subprog/func_call
 simplifications

On 29/03/18 23:44, Edward Cree wrote:
> By storing subprog boundaries as a subprogno mark on each insn, rather than
>  a start (and implicit end) for each subprog, we collect a number of gains:
> * More efficient determination of which subprog contains a given insn, and
>   thus of find_subprog (which subprog begins at a given insn).
> * Number of verifier "full recursive walk" passes is reduced, since most of
>   the work is done in the main insn walk (do_check()).  Leftover work in
>   other passes is mostly linear scans (O(insn_cnt)) or, in the case of
>   check_max_stack_depth(), a topological sort (O(subprog_cnt)).
>
> Some other changes were also included to support this:
> * Per-subprog info is stored in env->subprog_info, an array of structs,
>   rather than several arrays with a common index.
> * Call graph is now stored in the new bpf_subprog_info struct; used here
>   for check_max_stack_depth() but may have other uses too.
>
> Along with this, patch #3 puts parent pointers (used by liveness analysis)
>  in the registers instead of the func_state or verifier_state, so that we
>  don't need skip_callee() machinery.  This also does the right thing for
>  stack slots, so they don't need their own special handling for liveness
>  marking either.
Whoops, forgot to add:
Changes from v1:
* No longer allows non-contiguous subprogs.
* No longer allows LD_ABS|IND and pseudo-calls in the same prog.

> Edward Cree (3):
>   bpf/verifier: validate func_calls by marking at do_check() time
>   bpf/verifier: update selftests
>   bpf/verifier: per-register parent pointers
>
>  include/linux/bpf_verifier.h                |  32 +-
>  kernel/bpf/verifier.c                       | 631 +++++++++++++---------------
>  tools/testing/selftests/bpf/test_verifier.c |  51 ++-
>  3 files changed, 344 insertions(+), 370 deletions(-)
>