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authorDaniel Borkmann <daniel@iogearbox.net>2017-08-18 18:11:06 +0300
committerDavid S. Miller <davem@davemloft.net>2017-08-18 21:00:41 +0300
commit2110ba58303f0c2a03360c5f81fbe67ed312e7b9 (patch)
treeed5b08bc788e8d52ef9fd9d91735444b088cbfa4 /Documentation/sysctl/net.txt
parenta120d9ab65354727559b9db75ded8071b7ef19e2 (diff)
downloadlinux-2110ba58303f0c2a03360c5f81fbe67ed312e7b9.tar.xz
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Current context speaking of tcpdump filters is out of date these days, so lets improve the sysctl description for the BPF knobs a bit.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/net.txt')
-rw-r--r--Documentation/sysctl/net.txt37
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