linux-kernel - Re: [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier

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Message-ID: <5953B436.6030506@iogearbox.net>
Date:   Wed, 28 Jun 2017 15:50:46 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Edward Cree <ecree@...arflare.com>, davem@...emloft.net,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...com>
CC:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>
Subject: Re: [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier

Hi Edward,

On 06/27/2017 02:53 PM, Edward Cree wrote:
> This series simplifies alignment tracking, generalises bounds tracking and
>   fixes some bounds-tracking bugs in the BPF verifier.  Pointer arithmetic on
>   packet pointers, stack pointers, map value pointers and context pointers has
>   been unified, and bounds on these pointers are only checked when the pointer
>   is dereferenced.
> Operations on pointers which destroy all relation to the original pointer
>   (such as multiplies and shifts) are disallowed if !env->allow_ptr_leaks,
>   otherwise they convert the pointer to an unknown scalar and feed it to the
>   normal scalar arithmetic handling.
> Pointer types have been unified with the corresponding adjusted-pointer types
>   where those existed (e.g. PTR_TO_MAP_VALUE[_ADJ] or FRAME_PTR vs
>   PTR_TO_STACK); similarly, CONST_IMM and UNKNOWN_VALUE have been unified into
>   SCALAR_VALUE.
> Pointer types (except CONST_PTR_TO_MAP, PTR_TO_MAP_VALUE_OR_NULL and
>   PTR_TO_PACKET_END, which do not allow arithmetic) have a 'fixed offset' and
>   a 'variable offset'; the former is used when e.g. adding an immediate or a
>   known-constant register, as long as it does not overflow.  Otherwise the
>   latter is used, and any operation creating a new variable offset creates a
>   new 'id' (and, for PTR_TO_PACKET, clears the 'range').
> SCALAR_VALUEs use the 'variable offset' fields to track the range of possible
>   values; the 'fixed offset' should never be set on a scalar.
>
> As of patch 12/12, all tests of tools/testing/selftests/bpf/test_verifier
>   and tools/testing/selftests/bpf/test_align pass.
>
> v3: added a few more tests; removed RFC tags.

Did you also have a chance in the meantime to look at reducing complexity
along with your unification? I did run the cilium test suite with your
latest set from here and current # worst case processed insns that
verifier has to go through for cilium progs increases from ~53k we have
right now to ~76k. I'm a bit worried that this quickly gets us close to
the upper ~98k max limit starting to reject programs again. Alternative
is to bump the complexity limit again in near future once run into it,
but preferably there's a way to optimize it along with the rewrite? Do
you see any possibilities worth exploring?

> v2: fixed nfp build, made test_align pass again and extended it with a few
>   new tests (though still need to add more).
>
> Edward Cree (12):
>    selftests/bpf: add test for mixed signed and unsigned bounds checks
>    bpf/verifier: rework value tracking
>    nfp: change bpf verifier hooks to match new verifier data structures
>    bpf/verifier: track signed and unsigned min/max values
>    bpf/verifier: more concise register state logs for constant var_off
>    selftests/bpf: change test_verifier expectations
>    selftests/bpf: rewrite test_align
>    selftests/bpf: add a test to test_align
>    selftests/bpf: add test for bogus operations on pointers
>    selftests/bpf: don't try to access past MAX_PACKET_OFF in
>      test_verifier
>    selftests/bpf: add tests for subtraction & negative numbers
>    selftests/bpf: variable offset negative tests
>
>   drivers/net/ethernet/netronome/nfp/bpf/verifier.c |   24 +-
>   include/linux/bpf.h                               |   34 +-
>   include/linux/bpf_verifier.h                      |   56 +-
>   include/linux/tnum.h                              |   81 +
>   kernel/bpf/Makefile                               |    2 +-
>   kernel/bpf/tnum.c                                 |  180 ++
>   kernel/bpf/verifier.c                             | 1943 ++++++++++++---------
>   tools/testing/selftests/bpf/test_align.c          |  462 ++++-
>   tools/testing/selftests/bpf/test_verifier.c       |  293 ++--
>   9 files changed, 2034 insertions(+), 1041 deletions(-)
>   create mode 100644 include/linux/tnum.h
>   create mode 100644 kernel/bpf/tnum.c
>

Thanks,
Daniel