Re: [PATCH v2 3/5] ebpf: add a way to dump an eBPF program

[Michael Kerrisk (man-pages)]

Hi Tycho,

On 11 September 2015 at 02:21, Tycho Andersen
<tycho.andersen@xxxxxxxxxxxxx> wrote:
> This commit adds a way to dump eBPF programs. The initial implementation
> doesn't support maps, and therefore only allows dumping seccomp ebpf
> programs which themselves don't currently support maps.

Same broken record :-).

Cheers,

Michael


> v2: don't export a prog_id for the filter
>
> Signed-off-by: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx>
> CC: Kees Cook <keescook@xxxxxxxxxxxx>
> CC: Will Drewry <wad@xxxxxxxxxxxx>
> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> CC: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
> CC: Alexei Starovoitov <ast@xxxxxxxxxx>
> CC: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> ---
>  include/uapi/linux/bpf.h | 14 ++++++++++++++
>  kernel/bpf/syscall.c     | 41 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 631cdee..e037a76 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -107,6 +107,13 @@ enum bpf_cmd {
>          * returns fd or negative error
>          */
>         BPF_PROG_LOAD,
> +
> +       /* dump an existing bpf
> +        * err = bpf(BPF_PROG_DUMP, union bpf_attr *attr, u32 size)
> +        * Using attr->prog_fd, attr->dump_insn_cnt, attr->dump_insns
> +        * returns zero or negative error
> +        */
> +       BPF_PROG_DUMP,
>  };
>
>  enum bpf_map_type {
> @@ -161,6 +168,13 @@ union bpf_attr {
>                 __aligned_u64   log_buf;        /* user supplied buffer */
>                 __u32           kern_version;   /* checked when prog_type=kprobe */
>         };
> +
> +       struct { /* anonymous struct used by BPF_PROG_DUMP command */
> +               __u32           prog_fd;
> +               __u32           dump_insn_cnt;
> +               __aligned_u64   dump_insns;     /* user supplied buffer */
> +               __u8            gpl_compatible;
> +       };
>  } __attribute__((aligned(8)));
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index dc9b464..58ae9f4 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -586,6 +586,44 @@ free_prog:
>         return err;
>  }
>
> +static int bpf_prog_dump(union bpf_attr *attr, union bpf_attr __user *uattr)
> +{
> +       int ufd = attr->prog_fd;
> +       struct fd f = fdget(ufd);
> +       struct bpf_prog *prog;
> +       int ret = -EINVAL;
> +
> +       prog = get_prog(f);
> +       if (IS_ERR(prog))
> +               return PTR_ERR(prog);
> +
> +       /* For now, let's refuse to dump anything that isn't a seccomp program.
> +        * Other program types have support for maps, which our current dump
> +        * code doesn't support.
> +        */
> +       if (prog->type != BPF_PROG_TYPE_SECCOMP)
> +               goto out;
> +
> +       ret = -EFAULT;
> +       if (put_user(prog->len, &uattr->dump_insn_cnt))
> +               goto out;
> +
> +       if (put_user((u8) prog->gpl_compatible, &uattr->gpl_compatible))
> +               goto out;
> +
> +       if (attr->dump_insns) {
> +               u32 len = prog->len * sizeof(struct bpf_insn);
> +
> +               if (copy_to_user(u64_to_ptr(attr->dump_insns),
> +                                prog->insns, len) != 0)
> +                       goto out;
> +       }
> +
> +       ret = 0;
> +out:
> +       return ret;
> +}
> +
>  SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
>  {
>         union bpf_attr attr = {};
> @@ -650,6 +688,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
>         case BPF_PROG_LOAD:
>                 err = bpf_prog_load(&attr);
>                 break;
> +       case BPF_PROG_DUMP:
> +               err = bpf_prog_dump(&attr, uattr);
> +               break;
>         default:
>                 err = -EINVAL;
>                 break;
> --
> 2.1.4
>
> --
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-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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