netdev - Re: [RFC 4/4] bpf: Restrict Checmate bpf programs to current kernel ABI

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Date:	Thu, 04 Aug 2016 11:52:48 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Sargun Dhillon <sargun@...gun.me>, linux-kernel@...r.kernel.org
CC:	alexei.starovoitov@...il.com,
	linux-security-module@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC 4/4] bpf: Restrict Checmate bpf programs to current kernel
 ABI

On 08/04/2016 09:12 AM, Sargun Dhillon wrote:
> I think it makes sense to restrict Checmate to loading programs that have been
> compiled with the current kernel ABI. We can further stabilize the ABI, and
> perhaps lift this restriction later.
>
> Signed-off-by: Sargun Dhillon <sargun@...gun.me>
> ---
>   kernel/bpf/syscall.c         | 2 +-
>   samples/bpf/checmate1_kern.c | 3 ++-
>   2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 228f962..2a37b4d 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -741,7 +741,7 @@ static int bpf_prog_load(union bpf_attr *attr)
>   	if (attr->insn_cnt >= BPF_MAXINSNS)
>   		return -EINVAL;
>
> -	if (type == BPF_PROG_TYPE_KPROBE &&
> +	if ((type & (BPF_PROG_TYPE_KPROBE | BPF_PROG_TYPE_CHECMATE)) &&
>   	    attr->kern_version != LINUX_VERSION_CODE)

Btw, this check is correct, program types are not masks.

BPF_PROG_TYPE_KPROBE (== 2) and BPF_PROG_TYPE_CHECMATE (== 7) will now
require every type to have a version code ...

>   		return -EINVAL;
>
> diff --git a/samples/bpf/checmate1_kern.c b/samples/bpf/checmate1_kern.c
> index f78b66b..d4ec1fa 100644
> --- a/samples/bpf/checmate1_kern.c
> +++ b/samples/bpf/checmate1_kern.c
> @@ -3,6 +3,7 @@
>   #include <linux/in.h>
>   #include <linux/checmate.h>
>   #include "bpf_helpers.h"
> +#include <linux/version.h>
>
>   SEC("checmate")
>   int prog(struct checmate_ctx *ctx)
> @@ -24,4 +25,4 @@ int prog(struct checmate_ctx *ctx)
>   }
>
>   char _license[] SEC("license") = "GPL";
> -
> +u32 _version SEC("version") = LINUX_VERSION_CODE;
>