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![Daniel Borkmann](/assets/img/avatar_default.png)
Long standing issue with JITed programs is that stack traces from function tracing check whether a given address is kernel code through {__,}kernel_text_address(), which checks for code in core kernel, modules and dynamically allocated ftrace trampolines. But what is still missing is BPF JITed programs (interpreted programs are not an issue as __bpf_prog_run() will be attributed to them), thus when a stack trace is triggered, the code walking the stack won't see any of the JITed ones. The same for address correlation done from user space via reading /proc/kallsyms. This is read by tools like perf, but the latter is also useful for permanent live tracing with eBPF itself in combination with stack maps when other eBPF types are part of the callchain. See offwaketime example on dumping stack from a map. This work tries to tackle that issue by making the addresses and symbols known to the kernel. The lookup from *kernel_text_address() is implemented through a latched RB tree that can be read under RCU in fast-path that is also shared for symbol/size/offset lookup for a specific given address in kallsyms. The slow-path iteration through all symbols in the seq file done via RCU list, which holds a tiny fraction of all exported ksyms, usually below 0.1 percent. Function symbols are exported as bpf_prog_<tag>, in order to aide debugging and attribution. This facility is currently enabled for root-only when bpf_jit_kallsyms is set to 1, and disabled if hardening is active in any mode. The rationale behind this is that still a lot of systems ship with world read permissions on kallsyms thus addresses should not get suddenly exposed for them. If that situation gets much better in future, we always have the option to change the default on this. Likewise, unprivileged programs are not allowed to add entries there either, but that is less of a concern as most such programs types relevant in this context are for root-only anyway. If enabled, call graphs and stack traces will then show a correct attribution; one example is illustrated below, where the trace is now visible in tooling such as perf script --kallsyms=/proc/kallsyms and friends. Before: 7fff8166889d bpf_clone_redirect+0x80007f0020ed (/lib/modules/4.9.0-rc8+/build/vmlinux) f5d80 __sendmsg_nocancel+0xffff006451f1a007 (/usr/lib64/libc-2.18.so) After: 7fff816688b7 bpf_clone_redirect+0x80007f002107 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fffa0575728 bpf_prog_33c45a467c9e061a+0x8000600020fb (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fffa07ef1fc cls_bpf_classify+0x8000600020dc (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff81678b68 tc_classify+0x80007f002078 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8164d40b __netif_receive_skb_core+0x80007f0025fb (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8164d718 __netif_receive_skb+0x80007f002018 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8164e565 process_backlog+0x80007f002095 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8164dc71 net_rx_action+0x80007f002231 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff81767461 __softirqentry_text_start+0x80007f0020d1 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff817658ac do_softirq_own_stack+0x80007f00201c (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff810a2c20 do_softirq+0x80007f002050 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff810a2cb5 __local_bh_enable_ip+0x80007f002085 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8168d452 ip_finish_output2+0x80007f002152 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8168ea3d ip_finish_output+0x80007f00217d (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff8168f2af ip_output+0x80007f00203f (/lib/modules/4.9.0-rc8+/build/vmlinux) [...] 7fff81005854 do_syscall_64+0x80007f002054 (/lib/modules/4.9.0-rc8+/build/vmlinux) 7fff817649eb return_from_SYSCALL_64+0x80007f002000 (/lib/modules/4.9.0-rc8+/build/vmlinux) f5d80 __sendmsg_nocancel+0xffff01c484812007 (/usr/lib64/libc-2.18.so) Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Cc: linux-kernel@vger.kernel.org Signed-off-by: David S. Miller <davem@davemloft.net>
350 lines
13 KiB
Text
350 lines
13 KiB
Text
Documentation for /proc/sys/net/*
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(c) 1999 Terrehon Bowden <terrehon@pacbell.net>
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Bodo Bauer <bb@ricochet.net>
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(c) 2000 Jorge Nerin <comandante@zaralinux.com>
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(c) 2009 Shen Feng <shen@cn.fujitsu.com>
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For general info and legal blurb, please look in README.
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==============================================================
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This file contains the documentation for the sysctl files in
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/proc/sys/net
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The interface to the networking parts of the kernel is located in
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/proc/sys/net. The following table shows all possible subdirectories. You may
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see only some of them, depending on your kernel's configuration.
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Table : Subdirectories in /proc/sys/net
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..............................................................................
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Directory Content Directory Content
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core General parameter appletalk Appletalk protocol
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unix Unix domain sockets netrom NET/ROM
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802 E802 protocol ax25 AX25
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ethernet Ethernet protocol rose X.25 PLP layer
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ipv4 IP version 4 x25 X.25 protocol
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ipx IPX token-ring IBM token ring
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bridge Bridging decnet DEC net
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ipv6 IP version 6 tipc TIPC
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..............................................................................
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1. /proc/sys/net/core - Network core options
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-------------------------------------------------------
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bpf_jit_enable
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--------------
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This enables Berkeley Packet Filter Just in Time compiler.
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Currently supported on x86_64 architecture, bpf_jit provides a framework
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to speed packet filtering, the one used by tcpdump/libpcap for example.
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Values :
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0 - disable the JIT (default value)
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1 - enable the JIT
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2 - enable the JIT and ask the compiler to emit traces on kernel log.
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bpf_jit_harden
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--------------
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This enables hardening for the Berkeley Packet Filter Just in Time compiler.
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Supported are eBPF JIT backends. Enabling hardening trades off performance,
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but can mitigate JIT spraying.
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Values :
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0 - disable JIT hardening (default value)
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1 - enable JIT hardening for unprivileged users only
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2 - enable JIT hardening for all users
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bpf_jit_kallsyms
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----------------
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When Berkeley Packet Filter Just in Time compiler is enabled, then compiled
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images are unknown addresses to the kernel, meaning they neither show up in
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traces nor in /proc/kallsyms. This enables export of these addresses, which
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can be used for debugging/tracing. If bpf_jit_harden is enabled, this feature
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is disabled.
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Values :
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0 - disable JIT kallsyms export (default value)
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1 - enable JIT kallsyms export for privileged users only
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dev_weight
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--------------
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The maximum number of packets that kernel can handle on a NAPI interrupt,
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it's a Per-CPU variable.
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Default: 64
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dev_weight_rx_bias
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--------------
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RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
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of the driver for the per softirq cycle netdev_budget. This parameter influences
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the proportion of the configured netdev_budget that is spent on RPS based packet
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processing during RX softirq cycles. It is further meant for making current
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dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.
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(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based
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on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias).
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Default: 1
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dev_weight_tx_bias
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--------------
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Scales the maximum number of packets that can be processed during a TX softirq cycle.
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Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric
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net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog.
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Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias).
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Default: 1
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default_qdisc
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--------------
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The default queuing discipline to use for network devices. This allows
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overriding the default of pfifo_fast with an alternative. Since the default
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queuing discipline is created without additional parameters so is best suited
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to queuing disciplines that work well without configuration like stochastic
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fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use
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queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin
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which require setting up classes and bandwidths. Note that physical multiqueue
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interfaces still use mq as root qdisc, which in turn uses this default for its
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leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
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default to noqueue.
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Default: pfifo_fast
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busy_read
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----------------
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Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL)
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Approximate time in us to busy loop waiting for packets on the device queue.
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This sets the default value of the SO_BUSY_POLL socket option.
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Can be set or overridden per socket by setting socket option SO_BUSY_POLL,
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which is the preferred method of enabling. If you need to enable the feature
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globally via sysctl, a value of 50 is recommended.
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Will increase power usage.
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Default: 0 (off)
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busy_poll
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----------------
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Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL)
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Approximate time in us to busy loop waiting for events.
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Recommended value depends on the number of sockets you poll on.
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For several sockets 50, for several hundreds 100.
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For more than that you probably want to use epoll.
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Note that only sockets with SO_BUSY_POLL set will be busy polled,
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so you want to either selectively set SO_BUSY_POLL on those sockets or set
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sysctl.net.busy_read globally.
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Will increase power usage.
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Default: 0 (off)
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rmem_default
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------------
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The default setting of the socket receive buffer in bytes.
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rmem_max
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--------
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The maximum receive socket buffer size in bytes.
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tstamp_allow_data
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-----------------
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Allow processes to receive tx timestamps looped together with the original
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packet contents. If disabled, transmit timestamp requests from unprivileged
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processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
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Default: 1 (on)
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wmem_default
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------------
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The default setting (in bytes) of the socket send buffer.
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wmem_max
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--------
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The maximum send socket buffer size in bytes.
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message_burst and message_cost
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------------------------------
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These parameters are used to limit the warning messages written to the kernel
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log from the networking code. They enforce a rate limit to make a
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denial-of-service attack impossible. A higher message_cost factor, results in
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fewer messages that will be written. Message_burst controls when messages will
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be dropped. The default settings limit warning messages to one every five
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seconds.
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warnings
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--------
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This sysctl is now unused.
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This was used to control console messages from the networking stack that
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occur because of problems on the network like duplicate address or bad
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checksums.
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These messages are now emitted at KERN_DEBUG and can generally be enabled
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and controlled by the dynamic_debug facility.
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netdev_budget
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-------------
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Maximum number of packets taken from all interfaces in one polling cycle (NAPI
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poll). In one polling cycle interfaces which are registered to polling are
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probed in a round-robin manner.
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netdev_max_backlog
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------------------
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Maximum number of packets, queued on the INPUT side, when the interface
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receives packets faster than kernel can process them.
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netdev_rss_key
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--------------
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RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
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randomly generated.
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Some user space might need to gather its content even if drivers do not
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provide ethtool -x support yet.
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myhost:~# cat /proc/sys/net/core/netdev_rss_key
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84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total)
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File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
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Note:
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/proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
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but most drivers only use 40 bytes of it.
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myhost:~# ethtool -x eth0
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RX flow hash indirection table for eth0 with 8 RX ring(s):
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0: 0 1 2 3 4 5 6 7
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RSS hash key:
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84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8:43:e3:c9:0c:fd:17:55:c2:3a:4d:69:ed:f1:42:89
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netdev_tstamp_prequeue
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----------------------
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If set to 0, RX packet timestamps can be sampled after RPS processing, when
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the target CPU processes packets. It might give some delay on timestamps, but
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permit to distribute the load on several cpus.
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If set to 1 (default), timestamps are sampled as soon as possible, before
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queueing.
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optmem_max
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----------
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Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
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of struct cmsghdr structures with appended data.
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2. /proc/sys/net/unix - Parameters for Unix domain sockets
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-------------------------------------------------------
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There is only one file in this directory.
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unix_dgram_qlen limits the max number of datagrams queued in Unix domain
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socket's buffer. It will not take effect unless PF_UNIX flag is specified.
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3. /proc/sys/net/ipv4 - IPV4 settings
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-------------------------------------------------------
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Please see: Documentation/networking/ip-sysctl.txt and ipvs-sysctl.txt for
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descriptions of these entries.
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4. Appletalk
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-------------------------------------------------------
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The /proc/sys/net/appletalk directory holds the Appletalk configuration data
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when Appletalk is loaded. The configurable parameters are:
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aarp-expiry-time
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----------------
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The amount of time we keep an ARP entry before expiring it. Used to age out
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old hosts.
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aarp-resolve-time
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-----------------
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The amount of time we will spend trying to resolve an Appletalk address.
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aarp-retransmit-limit
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---------------------
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The number of times we will retransmit a query before giving up.
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aarp-tick-time
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--------------
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Controls the rate at which expires are checked.
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The directory /proc/net/appletalk holds the list of active Appletalk sockets
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on a machine.
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The fields indicate the DDP type, the local address (in network:node format)
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the remote address, the size of the transmit pending queue, the size of the
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received queue (bytes waiting for applications to read) the state and the uid
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owning the socket.
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/proc/net/atalk_iface lists all the interfaces configured for appletalk.It
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shows the name of the interface, its Appletalk address, the network range on
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that address (or network number for phase 1 networks), and the status of the
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interface.
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/proc/net/atalk_route lists each known network route. It lists the target
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(network) that the route leads to, the router (may be directly connected), the
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route flags, and the device the route is using.
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5. IPX
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-------------------------------------------------------
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The IPX protocol has no tunable values in proc/sys/net.
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The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
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socket giving the local and remote addresses in Novell format (that is
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network:node:port). In accordance with the strange Novell tradition,
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everything but the port is in hex. Not_Connected is displayed for sockets that
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are not tied to a specific remote address. The Tx and Rx queue sizes indicate
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the number of bytes pending for transmission and reception. The state
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indicates the state the socket is in and the uid is the owning uid of the
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socket.
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The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
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it gives the network number, the node number, and indicates if the network is
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the primary network. It also indicates which device it is bound to (or
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Internal for internal networks) and the Frame Type if appropriate. Linux
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supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
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IPX.
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The /proc/net/ipx_route table holds a list of IPX routes. For each route it
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gives the destination network, the router node (or Directly) and the network
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address of the router (or Connected) for internal networks.
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6. TIPC
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-------------------------------------------------------
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tipc_rmem
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----------
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The TIPC protocol now has a tunable for the receive memory, similar to the
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tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)
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# cat /proc/sys/net/tipc/tipc_rmem
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4252725 34021800 68043600
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#
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The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values
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are scaled (shifted) versions of that same value. Note that the min value
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is not at this point in time used in any meaningful way, but the triplet is
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preserved in order to be consistent with things like tcp_rmem.
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named_timeout
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--------------
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TIPC name table updates are distributed asynchronously in a cluster, without
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any form of transaction handling. This means that different race scenarios are
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possible. One such is that a name withdrawal sent out by one node and received
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by another node may arrive after a second, overlapping name publication already
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has been accepted from a third node, although the conflicting updates
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originally may have been issued in the correct sequential order.
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If named_timeout is nonzero, failed topology updates will be placed on a defer
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queue until another event arrives that clears the error, or until the timeout
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expires. Value is in milliseconds.
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