linux-kernel - Re: [PATCH bpf-next v6 4/5] selftests/bpf: Use vmlinux.h in socket_cookie

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Date:   Wed, 27 Jan 2021 12:57:34 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Florent Revest <revest@...omium.org>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        KP Singh <kpsingh@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        KP Singh <kpsingh@...nel.org>
Subject: Re: [PATCH bpf-next v6 4/5] selftests/bpf: Use vmlinux.h in socket_cookie_prog.c

On Tue, Jan 26, 2021 at 10:36 AM Florent Revest <revest@...omium.org> wrote:
>
> When migrating from the bpf.h's to the vmlinux.h's definition of struct
> bps_sock, an interesting LLVM behavior happened. LLVM started producing
> two fetches of ctx->sk in the sockops program this means that the
> verifier could not keep track of the NULL-check on ctx->sk. Therefore,
> we need to extract ctx->sk in a variable before checking and
> dereferencing it.
>
> Acked-by: KP Singh <kpsingh@...nel.org>
> Signed-off-by: Florent Revest <revest@...omium.org>
> ---

Acked-by: Andrii Nakryiko <andrii@...nel.org>


>  .../testing/selftests/bpf/progs/socket_cookie_prog.c  | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/socket_cookie_prog.c b/tools/testing/selftests/bpf/progs/socket_cookie_prog.c
> index 81e84be6f86d..fbd5eaf39720 100644
> --- a/tools/testing/selftests/bpf/progs/socket_cookie_prog.c
> +++ b/tools/testing/selftests/bpf/progs/socket_cookie_prog.c
> @@ -1,12 +1,13 @@
>  // SPDX-License-Identifier: GPL-2.0
>  // Copyright (c) 2018 Facebook
>
> -#include <linux/bpf.h>
> -#include <sys/socket.h>
> +#include "vmlinux.h"
>
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_endian.h>
>
> +#define AF_INET6 10
> +
>  struct socket_cookie {
>         __u64 cookie_key;
>         __u32 cookie_value;
> @@ -41,7 +42,7 @@ int set_cookie(struct bpf_sock_addr *ctx)
>  SEC("sockops")
>  int update_cookie(struct bpf_sock_ops *ctx)
>  {
> -       struct bpf_sock *sk;
> +       struct bpf_sock *sk = ctx->sk;
>         struct socket_cookie *p;
>
>         if (ctx->family != AF_INET6)
> @@ -50,10 +51,10 @@ int update_cookie(struct bpf_sock_ops *ctx)
>         if (ctx->op != BPF_SOCK_OPS_TCP_CONNECT_CB)
>                 return 1;
>
> -       if (!ctx->sk)
> +       if (!sk)
>                 return 1;
>
> -       p = bpf_sk_storage_get(&socket_cookies, ctx->sk, 0, 0);
> +       p = bpf_sk_storage_get(&socket_cookies, sk, 0, 0);
>         if (!p)
>                 return 1;
>
> --
> 2.30.0.280.ga3ce27912f-goog
>