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Date: Mon, 25 Feb 2019 15:14:38 -0800
From: Stanislav Fomichev <sdf@...ichev.me>
To: brakmo <brakmo@...com>
Cc: netdev <netdev@...r.kernel.org>, Martin Lau <kafai@...com>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Eric Dumazet <eric.dumazet@...il.com>,
Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 2/9] bpf: Add bpf helper bpf_tcp_enter_cwr
On 02/22, brakmo wrote:
> From: Martin KaFai Lau <kafai@...com>
>
> This patch adds a new bpf helper BPF_FUNC_tcp_enter_cwr
> "int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)".
> It is added to BPF_PROG_TYPE_CGROUP_SKB which can be attached
> to the egress path where the bpf prog is called by
> ip_finish_output() or ip6_finish_output(). The verifier
> ensures that the parameter must be a tcp_sock.
>
> This helper makes a tcp_sock enter CWR state. It can be used
> by a bpf_prog to manage egress network bandwidth limit per
> cgroupv2. A later patch will have a sample program to
> show how it can be used to limit bandwidth usage per cgroupv2.
>
> To ensure it is only called from BPF_CGROUP_INET_EGRESS, the
> attr->expected_attach_type must be specified as BPF_CGROUP_INET_EGRESS
> during load time if the prog uses this new helper.
> The newly added prog->enforce_expected_attach_type bit will also be set
> if this new helper is used. This bit is for backward compatibility reason
> because currently prog->expected_attach_type has been ignored in
> BPF_PROG_TYPE_CGROUP_SKB. During attach time,
> prog->expected_attach_type is only enforced if the
> prog->enforce_expected_attach_type bit is set.
> i.e. prog->expected_attach_type is only enforced if this new helper
> is used by the prog.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
> include/linux/bpf.h | 1 +
> include/linux/filter.h | 3 ++-
> include/uapi/linux/bpf.h | 9 ++++++++-
> kernel/bpf/syscall.c | 12 ++++++++++++
> kernel/bpf/verifier.c | 4 ++++
> net/core/filter.c | 25 +++++++++++++++++++++++++
> 6 files changed, 52 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d5ba2fc01af3..2d54ba7cf9dd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -195,6 +195,7 @@ enum bpf_arg_type {
> ARG_PTR_TO_SOCKET, /* pointer to bpf_sock */
> ARG_PTR_TO_SPIN_LOCK, /* pointer to bpf_spin_lock */
> ARG_PTR_TO_SOCK_COMMON, /* pointer to sock_common */
> + ARG_PTR_TO_TCP_SOCK, /* pointer to tcp_sock */
> };
>
> /* type of values returned from helper functions */
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index f32b3eca5a04..c6e878bdc5a6 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -510,7 +510,8 @@ struct bpf_prog {
> blinded:1, /* Was blinded */
> is_func:1, /* program is a bpf function */
> kprobe_override:1, /* Do we override a kprobe? */
> - has_callchain_buf:1; /* callchain buffer allocated? */
> + has_callchain_buf:1, /* callchain buffer allocated? */
> + enforce_expected_attach_type:1; /* Enforce expected_attach_type checking at attach time */
> enum bpf_prog_type type; /* Type of BPF program */
> enum bpf_attach_type expected_attach_type; /* For some prog types */
> u32 len; /* Number of filter blocks */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index bcdd2474eee7..95b5058fa945 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2359,6 +2359,12 @@ union bpf_attr {
> * Return
> * A **struct bpf_tcp_sock** pointer on success, or NULL in
> * case of failure.
> + *
> + * int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)
> + * Description
> + * Make a tcp_sock enter CWR state.
> + * Return
> + * 0 on success, or a negative error in case of failure.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -2457,7 +2463,8 @@ union bpf_attr {
> FN(spin_lock), \
> FN(spin_unlock), \
> FN(sk_fullsock), \
> - FN(tcp_sock),
> + FN(tcp_sock), \
> + FN(tcp_enter_cwr),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index ec7c552af76b..9a478f2875cd 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1482,6 +1482,14 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
> default:
> return -EINVAL;
> }
> + case BPF_PROG_TYPE_CGROUP_SKB:
> + switch (expected_attach_type) {
> + case BPF_CGROUP_INET_INGRESS:
> + case BPF_CGROUP_INET_EGRESS:
> + return 0;
> + default:
> + return -EINVAL;
> + }
> default:
> return 0;
> }
> @@ -1725,6 +1733,10 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
> case BPF_PROG_TYPE_CGROUP_SOCK:
> case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
> return attach_type == prog->expected_attach_type ? 0 : -EINVAL;
> + case BPF_PROG_TYPE_CGROUP_SKB:
> + return prog->enforce_expected_attach_type &&
> + prog->expected_attach_type != attach_type ?
> + -EINVAL : 0;
> default:
> return 0;
> }
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 1b9496c41383..95fb385c6f3c 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2424,6 +2424,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
> return -EFAULT;
> }
> meta->ptr_id = reg->id;
> + } else if (arg_type == ARG_PTR_TO_TCP_SOCK) {
> + expected_type = PTR_TO_TCP_SOCK;
> + if (type != expected_type)
> + goto err_type;
> } else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
> if (meta->func_id == BPF_FUNC_spin_lock) {
> if (process_spin_lock(env, regno, true))
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 97916eedfe69..ca57ef25279c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5426,6 +5426,24 @@ static const struct bpf_func_proto bpf_tcp_sock_proto = {
> .arg1_type = ARG_PTR_TO_SOCK_COMMON,
> };
>
> +BPF_CALL_1(bpf_tcp_enter_cwr, struct tcp_sock *, tp)
> +{
> + struct sock *sk = (struct sock *)tp;
> +
> + if (sk->sk_state == TCP_ESTABLISHED) {
> + tcp_enter_cwr(sk);
> + return 0;
> + }
> +
> + return -EINVAL;
> +}
> +
> +static const struct bpf_func_proto bpf_tcp_enter_cwr_proto = {
> + .func = bpf_tcp_enter_cwr,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_TCP_SOCK,
> +};
> #endif /* CONFIG_INET */
>
> bool bpf_helper_changes_pkt_data(void *func)
> @@ -5585,6 +5603,13 @@ cg_skb_func_proto(enum bpf_func_id func_id, struct bpf_prog *prog)
> #ifdef CONFIG_INET
> case BPF_FUNC_tcp_sock:
> return &bpf_tcp_sock_proto;
[...]
> + case BPF_FUNC_tcp_enter_cwr:
> + if (prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
> + prog->enforce_expected_attach_type = 1;
> + return &bpf_tcp_enter_cwr_proto;
Instead of this back and forth with enforce_expected_attach_type, can we
just do here:
if (prog->expected_attach_type == BPF_CGROUP_INET_EGRESS)
return &bpf_tcp_enter_cwr_proto;
else
return null;
Wouldn't it have the same effect?
> + } else {
> + return NULL;
> + }
> #endif
> default:
> return sk_filter_func_proto(func_id, prog);
> --
> 2.17.1
>
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