16.4. eBPF and XDP

16.4.1. Introduction

eBPF stands for extended BPF. This is an extended version of Berkeley Packet Filter available in recent Linux kernel versions.

It provides more advanced features with eBPF programs developed in C and capability to use structured data shared between kernel and userspace.

eBPF is used for three things in Suricata:

  • eBPF filter: any BPF like filter can be developed. An example of filter accepting only packet for some VLANs is provided. A bypass implementation is also provided.
  • eBPF load balancing: provide programmable load balancing. A simple ippair load balancing is provided.
  • XDP programs: suricata can load XDP programs. A bypass program is provided.

Bypass can be implemented in eBPF and XDP. The advantage of XDP is that the packets are dropped at the earliest stage possible. So performance is better. But bypassed packets don’t reach the network so you can’t use this on regular traffic but only on duplicated/sniffed traffic.

16.4.1.1. XDP

XDP provides another Linux native way of optimising Suricata’s performance on sniffing high speed networks.

XDP or eXpress Data Path provides a high performance, programmable network data path in the Linux kernel as part of the IO Visor Project. XDP provides bare metal packet processing at the lowest point in the software stack which makes it ideal for speed without compromising programmability. Furthermore, new functions can be implemented dynamically with the integrated fast path without kernel modification.

More info about XDP

16.4.2. Requirements

You will need a kernel that supports XDP and, for real performance improvement, a network card that support XDP in the driver.

Suricata XDP code has been tested with 4.13.10 but 4.15 or later is necessary to use all features like the CPU redirect map.

If you are using an Intel netword card, you will need to stay with in tree kernel NIC drivers. The out of tree drivers do not contain the XDP support.

Having a network card with support for RSS symmetric hashing is a good point or you will have to use the XDP CPU redirect map feature.

16.4.3. Prerequisites

This guide has been confirmed on Debian/Ubuntu “LTS” Linux.

16.4.3.1. Disable irqbalance

systemctl stop irqbalance
systemctl disable irqbalance

16.4.3.2. Kernel

You need to run a kernel 4.13 or newer.

16.4.3.3. Clang

Make sure you have clang (>=3.9) installed on the system

sudo apt-get install clang

16.4.3.4. libbpf

Suricata uses libbpf to interact with eBPF and XDP. This library is available in the Linux tree. Before Linux 4.16, a patched libbpf library is also needed:

git clone -b libbpf-release  https://github.com/regit/linux.git

If you have a recent enough kernel, you can skip this part.

Now, you can build and install the library

cd linux/tools/lib/bpf/
make && sudo make install

sudo make install_headers
sudo ldconfig

16.4.4. Compile and install Suricata

To get Suricata source, you can use the usual

git clone  https://github.com/OISF/suricata.git
cd suricata && git clone https://github.com/OISF/libhtp.git -b 0.5.x

./autogen.sh

Then you need to add the ebpf flags to configure

CC=clang ./configure --prefix=/usr/ --sysconfdir=/etc/ --localstatedir=/var/ \
--enable-ebpf --enable-ebpf-build

make clean && make
sudo  make install-full
sudo ldconfig
sudo mkdir /etc/suricata/ebpf/

16.4.5. Setup bypass

If you plan to use eBPF or XDP for a kernel/hardware level bypass, you need to do the following:

First, enable bypass in the stream section

stream:
  bypass: true

If you want, you can also bypass encrypted flows by setting no-reassemble to yes in the app-layer tls section

app-layer:
  protocols:
    tls:
      enabled: yes
      detection-ports:
        dp: 443

      # Completely stop processing TLS/SSL session after the handshake
      # completed. If bypass is enabled this will also trigger flow
      # bypass. If disabled (the default), TLS/SSL session is still
      # tracked for Heartbleed and other anomalies.
      no-reassemble: yes

16.4.6. Setup eBPF filter

The file ebpf/vlan_filter.c contains a list of vlan id in a switch that you need to edit to get something adapted to your network. Another really basic filter dropping IPv6 packets is also available in ebpf/filter.c.

Suricata can load as eBPF filter any eBPF code exposing a filter section.

Once modifications and build via make are done, you can copy the resulting eBPF filter as needed

cp ebpf/vlan_filter.bpf /etc/suricata/ebpf/

Then setup the ebpf-filter-file variable in af-packet section

- interface: eth3
  threads: 16
  cluster-id: 97
  cluster-type: cluster_flow # choose any type suitable
  defrag: yes
  # eBPF file containing a 'loadbalancer' function that will be inserted into the
  # kernel and used as load balancing function
  ebpf-filter-file:  /etc/suricata/ebpf/vlan_filter.bpf
  use-mmap: yes
  ring-size: 200000

You can then run suricata normally

/usr/bin/suricata --pidfile /var/run/suricata.pid  --af-packet=eth3 -vvv

16.4.7. Setup eBPF bypass

You can also use eBPF bypass. To do that load the bypass_filter.bpf file and update af-packet configuration to set bypass to yes

- interface: eth3
  threads: 16
  cluster-id: 97
  cluster-type: cluster_qm # symmetric RSS hashing is mandatory to use this mode
  # eBPF file containing a 'filter' function that will be inserted into the
  # kernel and used as packet filter function
  ebpf-filter-file:  /etc/suricata/ebpf/bypass_filter.bpf
  bypass: yes
  use-mmap: yes
  ring-size: 200000

Constraints on eBPF code to have a bypass compliant code are stronger than for regular filter. The filter must expose flow_table_v4 and flow_table_v6 per CPU array maps with similar definitions as the one available in bypass_filter.c. These two maps will be accessed and maintained by Suricata to handle the lists of flow to bypass.

16.4.8. Setup eBPF load balancing

eBPF load balancing allows to load balance the traffic on the listening sockets With any logic implemented in the eBPF filter. The value returned by the function tagged with the loadbalancer section is used with a modulo on the CPU count to know in which socket the packet has to be send.

An implementation of a simple IP pair hashing function is provided in the lb.bpf file.

Copy the resulting eBPF filter as needed

cp ebpf/lb.bpf /etc/suricata/ebpf/

Then use cluster_ebpf as load balancing method in the interface section of af-packet and point the ebpf-lb-file variable to the lb.bpf file

- interface: eth3
  threads: 16
  cluster-id: 97
  cluster-type: cluster_ebpf
  defrag: yes
  # eBPF file containing a 'loadbalancer' function that will be inserted into the
  # kernel and used as load balancing function
  ebpf-lb-file:  /etc/suricata/ebpf/lb.bpf
  use-mmap: yes
  ring-size: 200000

16.4.9. Setup XDP bypass

XDP bypass will allow Suricata to tell the kernel that packets for some flows have to be dropped via the XDP mechanism. This is a really early drop that occurs before the datagram is reaching the Linux kernel network stack.

Linux 4.15 or newer are recommended to use that feature. You can use it on older kernel if you set BUILD_CPUMAP to 0 in ebpf/xdp_filter.c.

Copy the resulting xdp filter as needed:

cp ebpf/xdp_filter.bpf /etc/suricata/ebpf/

Setup af-packet section/interface in suricata.yaml.

We will use cluster_qm as we have symmetric hashing on the NIC, xdp-mode: driver and we will also use the /etc/suricata/ebpf/xdp_filter.bpf (in our example TCP offloading/bypass)

- interface: eth3
  threads: 16
  cluster-id: 97
  cluster-type: cluster_qm # symmetric hashing is a must!
  defrag: yes
  # Xdp mode, "soft" for skb based version, "driver" for network card based
  # and "hw" for card supporting eBPF.
  xdp-mode: driver
  xdp-filter-file:  /etc/suricata/ebpf/xdp_filter.bpf
  # if the ebpf filter implements a bypass function, you can set 'bypass' to
  # yes and benefit from these feature
  bypass: yes
  use-mmap: yes
  ring-size: 200000

XDP bypass is compatible with AF_PACKET IPS mode. Packets from bypassed flows will be send directly from one card to the second card without going by the kernel network stack.

16.4.9.1. Setup symmetric hashing on the NIC

Intel network card don’t support symmetric hashing but it is possible to emulate it by using a specific hashing function.

Follow these instructions closely for desired result:

ifconfig eth3 down

Use in tree kernel drivers: XDP support is not available in Intel drivers available on Intel website.

Enable symmetric hashing

ifconfig eth3 down
ethtool -L eth3 combined 16 # if you have at least 16 cores
ethtool -K eth3 rxhash on
ethtool -K eth3 ntuple on
ifconfig eth3 up
./set_irq_affinity 0-15 eth3
ethtool -X eth3 hkey 6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A equal 16
ethtool -x eth3
ethtool -n eth3

In the above setup you are free to use any recent set_irq_affinity script. It is available in any Intel x520/710 NIC sources driver download.

NOTE: We use a special low entropy key for the symmetric hashing. More info about the research for symmetric hashing set up

16.4.9.2. Disable any NIC offloading

Run the following command to disable offloading

for i in rx tx tso ufo gso gro lro tx nocache copy sg txvlan rxvlan; do
       /sbin/ethtool -K eth3 $i off 2>&1 > /dev/null;
done

16.4.9.3. Balance as much as you can

Try to use the network’s card balancing as much as possible

for proto in tcp4 udp4 ah4 esp4 sctp4 tcp6 udp6 ah6 esp6 sctp6; do
       /sbin/ethtool -N eth3 rx-flow-hash $proto sdfn
done

16.4.9.4. The XDP CPU redirect case

If ever your hardware is not able to do a symmetric load balancing but support XDP in driver mode, you can then use the CPU redirect map support available in the xdp_filter.bpf file. In this mode, the load balancing will be done by the XDP filter and each CPU will handle the whole packet treatment including the creation of the skb structure in kernel.

You will need Linux 4.15 or newer to use that feature.

To do so set the xdp-cpu-redirect variable in af-packet interface configuration to a set of CPUs. Then use the cluster_cpu as load balancing function. You will also need to set the affinity accordingly.

It is possible to use xdp_monitor to have information about the behavior of CPU redirect. This program is available in Linux tree under the samples/bpf directory and will be build by the make command. Sample output is the following

sudo ./xdp_monitor --stats
XDP-event       CPU:to  pps          drop-pps     extra-info
XDP_REDIRECT    11      2,880,212    0            Success
XDP_REDIRECT    total   2,880,212    0            Success
XDP_REDIRECT    total   0            0            Error
cpumap-enqueue   11:0   575,954      0            5.27       bulk-average
cpumap-enqueue  sum:0   575,954      0            5.27       bulk-average
cpumap-kthread  0       575,990      0            56,409     sched
cpumap-kthread  1       576,090      0            54,897     sched

16.4.9.5. Start Suricata with XDP

You can now start Suricata with XDP bypass activated

/usr/bin/suricata -c /etc/suricata/xdp-suricata.yaml --pidfile /var/run/suricata.pid  --af-packet=eth3 -vvv

Confirm you have the XDP filter engaged in the output (example):

...
...
(runmode-af-packet.c:220) <Config> (ParseAFPConfig) -- Enabling locked memory for mmap on iface eth3
(runmode-af-packet.c:231) <Config> (ParseAFPConfig) -- Enabling tpacket v3 capture on iface eth3
(runmode-af-packet.c:326) <Config> (ParseAFPConfig) -- Using queue based cluster mode for AF_PACKET (iface eth3)
(runmode-af-packet.c:424) <Info> (ParseAFPConfig) -- af-packet will use '/etc/suricata/ebpf/xdp_filter.bpf' as XDP filter file
(runmode-af-packet.c:429) <Config> (ParseAFPConfig) -- Using bypass kernel functionality for AF_PACKET (iface eth3)
(runmode-af-packet.c:609) <Config> (ParseAFPConfig) -- eth3: enabling zero copy mode by using data release call
(util-runmodes.c:296) <Info> (RunModeSetLiveCaptureWorkersForDevice) -- Going to use 8 thread(s)
...
...

16.4.10. Getting live info about bypass

You can get information about bypass via the stats event and through the unix socket. ìface-stat will return the number of bypassed packets (adding packets for a flow when it timeout). ebpf-bypassed-stats command will return the number of element in IPv4 and IPv6 flow tables for each interfaces.