diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2017-08-18 17:11:06 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-08-18 11:00:41 -0700 |
| commit | 2110ba58303f0c2a03360c5f81fbe67ed312e7b9 (patch) | |
| tree | ed5b08bc788e8d52ef9fd9d91735444b088cbfa4 /Documentation/sysctl | |
| parent | a120d9ab65354727559b9db75ded8071b7ef19e2 (diff) | |
bpf, doc: improve sysctl knob description
Current context speaking of tcpdump filters is out of date these
days, so lets improve the sysctl description for the BPF knobs
a bit.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/sysctl')
| -rw-r--r-- | Documentation/sysctl/net.txt | 37 |
1 files changed, 23 insertions, 14 deletions
diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index b9c3c6078010..d7c2b88b92ae 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -35,23 +35,32 @@ Table : Subdirectories in /proc/sys/net bpf_jit_enable -------------- -This enables Berkeley Packet Filter Just in Time compiler. - -There are two flavors of JIT, the new eBPF JIT supported on: +This enables the BPF Just in Time (JIT) compiler. BPF is a flexible +and efficient infrastructure allowing to execute bytecode at various +hook points. It is used in a number of Linux kernel subsystems such +as networking (e.g. XDP, tc), tracing (e.g. kprobes, uprobes, tracepoints) +and security (e.g. seccomp). LLVM has a BPF back end that can compile +restricted C into a sequence of BPF instructions. After program load +through bpf(2) and passing a verifier in the kernel, a JIT will then +translate these BPF proglets into native CPU instructions. There are +two flavors of JITs, the newer eBPF JIT currently supported on: - x86_64 - arm64 - ppc64 - sparc64 - mips64 -And the older cBPF JIT supported on: +And the older cBPF JIT supported on the following archs: - arm - mips - ppc - sparc -The BPF JIT provides a framework to speed packet filtering, the one used by -tcpdump/libpcap for example. +eBPF JITs are a superset of cBPF JITs, meaning the kernel will +migrate cBPF instructions into eBPF instructions and then JIT +compile them transparently. Older cBPF JITs can only translate +tcpdump filters, seccomp rules, etc, but not mentioned eBPF +programs loaded through bpf(2). Values : 0 - disable the JIT (default value) @@ -61,9 +70,9 @@ Values : bpf_jit_harden -------------- -This enables hardening for the Berkeley Packet Filter Just in Time compiler. -Supported are eBPF JIT backends. Enabling hardening trades off performance, -but can mitigate JIT spraying. +This enables hardening for the BPF JIT compiler. Supported are eBPF +JIT backends. Enabling hardening trades off performance, but can +mitigate JIT spraying. Values : 0 - disable JIT hardening (default value) 1 - enable JIT hardening for unprivileged users only @@ -72,11 +81,11 @@ Values : bpf_jit_kallsyms ---------------- -When Berkeley Packet Filter Just in Time compiler is enabled, then compiled -images are unknown addresses to the kernel, meaning they neither show up in -traces nor in /proc/kallsyms. This enables export of these addresses, which -can be used for debugging/tracing. If bpf_jit_harden is enabled, this feature -is disabled. +When BPF JIT compiler is enabled, then compiled images are unknown +addresses to the kernel, meaning they neither show up in traces nor +in /proc/kallsyms. This enables export of these addresses, which can +be used for debugging/tracing. If bpf_jit_harden is enabled, this +feature is disabled. Values : 0 - disable JIT kallsyms export (default value) 1 - enable JIT kallsyms export for privileged users only |