netdev - Re: [PATCH bpf-next v4 14/16] selftests/bpf: Add verifier tests for bpf_sk

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Date:   Wed, 15 Jul 2020 19:13:29 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH bpf-next v4 14/16] selftests/bpf: Add verifier tests for
 bpf_sk_lookup context access

On Mon, Jul 13, 2020 at 10:48 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> Exercise verifier access checks for bpf_sk_lookup context fields.
>
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
>

LGTM.

Acked-by: Andrii Nakryiko <andriin@...com>

> Notes:
>     v4:
>     - Bring back tests for narrow loads.
>
>     v3:
>     - Consolidate ACCEPT tests into one.
>     - Deduplicate REJECT tests and arrange them into logical groups.
>     - Add tests for out-of-bounds and unaligned access.
>     - Cover access to newly introduced 'sk' field.
>
>     v2:
>      - Adjust for fields renames in struct bpf_sk_lookup.
>
>  .../selftests/bpf/verifier/ctx_sk_lookup.c    | 471 ++++++++++++++++++
>  1 file changed, 471 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/verifier/ctx_sk_lookup.c
>

[...]

> +               /* 1-byte read from local_port field */
> +               BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port)),
> +               BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port) + 1),
> +               BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port) + 2),
> +               BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port) + 3),
> +               /* 2-byte read from local_port field */
> +               BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port)),
> +               BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port) + 2),
> +               /* 4-byte read from local_port field */
> +               BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, local_port)),
> +
> +               /* 8-byte read from sk field */
> +               BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, sk)),
> +               BPF_EXIT_INSN(),
> +       },
> +       .result = ACCEPT,
> +       .prog_type = BPF_PROG_TYPE_SK_LOOKUP,
> +       .expected_attach_type = BPF_SK_LOOKUP,
> +},

This looks like a common class of tests which can be auto-generated
just from the list of fields and their sizes. Something for someone's
wishlist, though.

> +/* invalid 8-byte reads from a 4-byte fields in bpf_sk_lookup */
> +{
> +       "invalid 8-byte read from bpf_sk_lookup family field",
> +       .insns = {
> +               BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
> +                           offsetof(struct bpf_sk_lookup, family)),
> +               BPF_EXIT_INSN(),
> +       },
> +       .errstr = "invalid bpf_context access",
> +       .result = REJECT,
> +       .prog_type = BPF_PROG_TYPE_SK_LOOKUP,
> +       .expected_attach_type = BPF_SK_LOOKUP,
> +},

[...]