Note: this is more of an RFC... question in patch format... is this
even a good idea?
On Tue, Nov 23, 2021 at 12:56 PM Maciej Żenczykowski
<zenczykowski@xxxxxxxxx> wrote:
>
> From: Maciej Żenczykowski <maze@xxxxxxxxxx>
>
> skfilter bpf programs can read the packet directly via llvm.bpf.load.byte/
> /half/word which are 8/16/32-bit primitive bpf instructions and thus
> behave basically as well as DPA reads. But there is no 64-bit equivalent,
> due to the support for the equivalent 64-bit bpf opcode never having been
> added (unclear why, there was a patch posted).
> DPA uses a slightly different mechanism, so doesn't suffer this limitation.
>
> Using 64-bit reads, 128-bit ipv6 address comparisons can be done in just
> 2 steps, instead of the 4 steps needed with llvm.bpf.word.
>
> This should hopefully allow simpler (less instructions, and possibly less
> logic and maybe even less jumps) programs. Less jumps may also mean vastly
> faster bpf verifier times (it can be exponential in the number of jumps...).
>
> This can be particularly important when trying to do something like scan
> a netlink message for a pattern (2000 iteration loop) to decide whether
> a message should be dropped, or delivered to userspace (thus waking it up).
>
> I'm requiring CAP_NET_ADMIN because I'm not sure of the security
> implications...
>
> Tested: only build tested
> Signed-off-by: Maciej Żenczykowski <maze@xxxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 331b170d9fcc..0c2e25fb9844 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3258,6 +3258,11 @@ static bool may_access_direct_pkt_data(struct bpf_verifier_env *env,
> enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
>
> switch (prog_type) {
> + case BPF_PROG_TYPE_SOCKET_FILTER:
> + if (meta || !capable(CAP_NET_ADMIN))
> + return false;
> + fallthrough;
> +
> /* Program types only with direct read access go here! */
> case BPF_PROG_TYPE_LWT_IN:
> case BPF_PROG_TYPE_LWT_OUT:
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
