| Message ID | 20180312192339.8039.54134.stgit@john-Precision-Tower-5810 |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf,sockmap: sendmsg/sendfile ULP | expand |
From: John Fastabend <john.fastabend@gmail.com> Date: Mon, 12 Mar 2018 12:23:39 -0700 > In the case where we need a specific number of bytes before a > verdict can be assigned, even if the data spans multiple sendmsg > or sendfile calls. The BPF program may use msg_cork_bytes(). > > The extreme case is a user can call sendmsg repeatedly with > 1-byte msg segments. Obviously, this is bad for performance but > is still valid. If the BPF program needs N bytes to validate > a header it can use msg_cork_bytes to specify N bytes and the > BPF program will not be called again until N bytes have been > accumulated. The infrastructure will attempt to coalesce data > if possible so in many cases (most my use cases at least) the > data will be in a single scatterlist element with data pointers > pointing to start/end of the element. However, this is dependent > on available memory so is not guaranteed. So BPF programs must > validate data pointer ranges, but this is the case anyways to > convince the verifier the accesses are valid. > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> Acked-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index e50c61f..cfcc002 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -770,7 +770,8 @@ enum bpf_attach_type { FN(override_return), \ FN(sock_ops_cb_flags_set), \ FN(msg_redirect_map), \ - FN(msg_apply_bytes), + FN(msg_apply_bytes), \ + FN(msg_cork_bytes), /* integer value in 'imm' field of BPF_CALL instruction selects which helper * function eBPF program intends to call diff --git a/net/core/filter.c b/net/core/filter.c index df2a8f4..2c73af0 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -1942,6 +1942,20 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg) .arg2_type = ARG_ANYTHING, }; +BPF_CALL_2(bpf_msg_cork_bytes, struct sk_msg_buff *, msg, u64, bytes) +{ + msg->cork_bytes = bytes; + return 0; +} + +static const struct bpf_func_proto bpf_msg_cork_bytes_proto = { + .func = bpf_msg_cork_bytes, + .gpl_only = false, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_CTX, + .arg2_type = ARG_ANYTHING, +}; + BPF_CALL_1(bpf_get_cgroup_classid, const struct sk_buff *, skb) { return task_get_classid(skb); @@ -3650,6 +3664,8 @@ static const struct bpf_func_proto *sk_msg_func_proto(enum bpf_func_id func_id) return &bpf_msg_redirect_map_proto; case BPF_FUNC_msg_apply_bytes: return &bpf_msg_apply_bytes_proto; + case BPF_FUNC_msg_cork_bytes: + return &bpf_msg_cork_bytes_proto; default: return bpf_base_func_proto(func_id); }
In the case where we need a specific number of bytes before a verdict can be assigned, even if the data spans multiple sendmsg or sendfile calls. The BPF program may use msg_cork_bytes(). The extreme case is a user can call sendmsg repeatedly with 1-byte msg segments. Obviously, this is bad for performance but is still valid. If the BPF program needs N bytes to validate a header it can use msg_cork_bytes to specify N bytes and the BPF program will not be called again until N bytes have been accumulated. The infrastructure will attempt to coalesce data if possible so in many cases (most my use cases at least) the data will be in a single scatterlist element with data pointers pointing to start/end of the element. However, this is dependent on available memory so is not guaranteed. So BPF programs must validate data pointer ranges, but this is the case anyways to convince the verifier the accesses are valid. Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- include/uapi/linux/bpf.h | 3 ++- net/core/filter.c | 16 ++++++++++++++++ 2 files changed, 18 insertions(+), 1 deletion(-)