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Jesper Dangaard Brouer 6cc16d6401 bpf: Add BPF-helper for MTU checking 
This BPF-helper bpf_check_mtu() works for both XDP and TC-BPF programs.

The SKB object is complex and the skb->len value (accessible from
BPF-prog) also include the length of any extra GRO/GSO segments, but
without taking into account that these GRO/GSO segments get added
transport (L4) and network (L3) headers before being transmitted. Thus,
this BPF-helper is created such that the BPF-programmer don't need to
handle these details in the BPF-prog.

The API is designed to help the BPF-programmer, that want to do packet
context size changes, which involves other helpers. These other helpers
usually does a delta size adjustment. This helper also support a delta
size (len_diff), which allow BPF-programmer to reuse arguments needed by
these other helpers, and perform the MTU check prior to doing any actual
size adjustment of the packet context.

It is on purpose, that we allow the len adjustment to become a negative
result, that will pass the MTU check. This might seem weird, but it's not
this helpers responsibility to "catch" wrong len_diff adjustments. Other
helpers will take care of these checks, if BPF-programmer chooses to do
actual size adjustment.

V14:
 - Improve man-page desc of len_diff.

V13:
 - Enforce flag BPF_MTU_CHK_SEGS cannot use len_diff.

V12:
 - Simplify segment check that calls skb_gso_validate_network_len.
 - Helpers should return long

V9:
- Use dev->hard_header_len (instead of ETH_HLEN)
- Annotate with unlikely req from Daniel
- Fix logic error using skb_gso_validate_network_len from Daniel

V6:
- Took John's advice and dropped BPF_MTU_CHK_RELAX
- Returned MTU is kept at L3-level (like fib_lookup)

V4: Lot of changes
 - ifindex 0 now use current netdev for MTU lookup
 - rename helper from bpf_mtu_check to bpf_check_mtu
 - fix bug for GSO pkt length (as skb->len is total len)
 - remove __bpf_len_adj_positive, simply allow negative len adj

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/161287790461.790810.3429728639563297353.stgit@firesoul
2021-03-03 08:35:13 -08:00
include bpf: Add BPF-helper for MTU checking 2021-03-03 08:35:13 -08:00
scripts sync: ignore libc_compat.h 2020-10-12 12:18:53 -07:00
src libbpf: Ignore non function pointer member in struct_ops 2021-03-03 08:35:13 -08:00
travis-ci travis-ci: switch from GCC8 to GCC10 2021-02-22 14:00:53 -08:00
.lgtm.yml lgtm: fix the extraction process 2019-10-28 15:15:47 -07:00
.travis.yml travis-ci: switch from GCC8 to GCC10 2021-02-22 14:00:53 -08:00
BPF-CHECKPOINT-COMMIT sync: latest libbpf changes from kernel 2021-01-26 19:32:13 -08:00
CHECKPOINT-COMMIT sync: latest libbpf changes from kernel 2021-01-26 19:32:13 -08:00
LICENSE license: add LICENSE with dual-license SPDX expression 2019-11-26 11:06:43 -08:00
LICENSE.BSD-2-Clause libbpf: add BSD-2-Clause and LGPL-2.1 licenses 2019-11-26 09:54:43 -08:00
LICENSE.LGPL-2.1 fix typo in license name 2021-02-22 11:35:49 -08:00
README.md README: mention that Debian 11 ships with BTF support 2021-01-22 12:27:35 -08:00

README.md

BPF/libbpf usage and questions

Please check out libbpf-bootstrap and the companion blog post for the examples of building BPF applications with libbpf. libbpf-tools are also a good source of the real-world libbpf-based tracing tools.

All general BPF questions, including kernel functionality, libbpf APIs and their application, should be sent to bpf@vger.kernel.org mailing list. You can subscribe to it here and search its archive here. Please search the archive before asking new questions. It very well might be that this was already addressed or answered before.

bpf@vger.kernel.org is monitored by many more people and they will happily try to help you with whatever issue you have. This repository's PRs and issues should be opened only for dealing with issues pertaining to specific way this libbpf mirror repo is set up and organized.

Build Build Status Total alerts Coverity

libelf is an internal dependency of libbpf and thus it is required to link against and must be installed on the system for applications to work. pkg-config is used by default to find libelf, and the program called can be overridden with PKG_CONFIG.

If using pkg-config at build time is not desired, it can be disabled by setting NO_PKG_CONFIG=1 when calling make.

To build both static libbpf.a and shared libbpf.so:

$ cd src
$ make

To build only static libbpf.a library in directory build/ and install them together with libbpf headers in a staging directory root/:

$ cd src
$ mkdir build root
$ BUILD_STATIC_ONLY=y OBJDIR=build DESTDIR=root make install

To build both static libbpf.a and shared libbpf.so against a custom libelf dependency installed in /build/root/ and install them together with libbpf headers in a build directory /build/root/:

$ cd src
$ PKG_CONFIG_PATH=/build/root/lib64/pkgconfig DESTDIR=/build/root make install

Distributions

Distributions packaging libbpf from this mirror:

Benefits of packaging from the mirror over packaging from kernel sources:

  • Consistent versioning across distributions.
  • No ties to any specific kernel, transparent handling of older kernels. Libbpf is designed to be kernel-agnostic and work across multitude of kernel versions. It has built-in mechanisms to gracefully handle older kernels, that are missing some of the features, by working around or gracefully degrading functionality. Thus libbpf is not tied to a specific kernel version and can/should be packaged and versioned independently.
  • Continuous integration testing via TravisCI.
  • Static code analysis via LGTM and Coverity.

Package dependencies of libbpf, package names may vary across distros:

  • zlib
  • libelf

BPF CO-RE (Compile Once – Run Everywhere)

Libbpf supports building BPF CO-RE-enabled applications, which, in contrast to BCC, do not require Clang/LLVM runtime being deployed to target servers and doesn't rely on kernel-devel headers being available.

It does rely on kernel to be built with BTF type information, though. Some major Linux distributions come with kernel BTF already built in:

  • Fedora 31+
  • RHEL 8.2+
  • OpenSUSE Tumbleweed (in the next release, as of 2020-06-04)
  • Arch Linux (from kernel 5.7.1.arch1-1)
  • Ubuntu 20.10
  • Debian 11 (amd64/arm64)

If your kernel doesn't come with BTF built-in, you'll need to build custom kernel. You'll need:

  • pahole 1.16+ tool (part of dwarves package), which performs DWARF to BTF conversion;
  • kernel built with CONFIG_DEBUG_INFO_BTF=y option;
  • you can check if your kernel has BTF built-in by looking for /sys/kernel/btf/vmlinux file:
$ ls -la /sys/kernel/btf/vmlinux
-r--r--r--. 1 root root 3541561 Jun  2 18:16 /sys/kernel/btf/vmlinux

To develop and build BPF programs, you'll need Clang/LLVM 10+. The following distributions have Clang/LLVM 10+ packaged by default:

  • Fedora 32+
  • Ubuntu 20.04+
  • Arch Linux
  • Ubuntu 20.10 (LLVM 11)
  • Debian 11 (LLVM 11)

Otherwise, please make sure to update it on your system.

The following resources are useful to understand what BPF CO-RE is and how to use it:

Details

This is a mirror of bpf-next Linux source tree's tools/lib/bpf directory plus its supporting header files.

All the gory details of syncing can be found in scripts/sync-kernel.sh script.

Some header files in this repo (include/linux/*.h) are reduced versions of their counterpart files at bpf-next's tools/include/linux/*.h to make compilation successful.

License

This work is dual-licensed under BSD 2-clause license and GNU LGPL v2.1 license. You can choose between one of them if you use this work.

SPDX-License-Identifier: BSD-2-Clause OR LGPL-2.1