6b90604fa7
Recently, user ringbuf support introduced a PTR_TO_DYNPTR register type
for use in callback state, because in case of user ringbuf helpers,
there is no dynptr on the stack that is passed into the callback. To
reflect such a state, a special register type was created.
However, some checks have been bypassed incorrectly during the addition
of this feature. First, for arg_type with MEM_UNINIT flag which
initialize a dynptr, they must be rejected for such register type.
Secondly, in the future, there are plans to add dynptr helpers that
operate on the dynptr itself and may change its offset and other
properties.
In all of these cases, PTR_TO_DYNPTR shouldn't be allowed to be passed
to such helpers, however the current code simply returns 0.
The rejection for helpers that release the dynptr is already handled.
For fixing this, we take a step back and rework existing code in a way
that will allow fitting in all classes of helpers and have a coherent
model for dealing with the variety of use cases in which dynptr is used.
First, for ARG_PTR_TO_DYNPTR, it can either be set alone or together
with a DYNPTR_TYPE_* constant that denotes the only type it accepts.
Next, helpers which initialize a dynptr use MEM_UNINIT to indicate this
fact. To make the distinction clear, use MEM_RDONLY flag to indicate
that the helper only operates on the memory pointed to by the dynptr,
not the dynptr itself. In C parlance, it would be equivalent to taking
the dynptr as a point to const argument.
When either of these flags are not present, the helper is allowed to
mutate both the dynptr itself and also the memory it points to.
Currently, the read only status of the memory is not tracked in the
dynptr, but it would be trivial to add this support inside dynptr state
of the register.
With these changes and renaming PTR_TO_DYNPTR to CONST_PTR_TO_DYNPTR to
better reflect its usage, it can no longer be passed to helpers that
initialize a dynptr, i.e. bpf_dynptr_from_mem, bpf_ringbuf_reserve_dynptr.
A note to reviewers is that in code that does mark_stack_slots_dynptr,
and unmark_stack_slots_dynptr, we implicitly rely on the fact that
PTR_TO_STACK reg is the only case that can reach that code path, as one
cannot pass CONST_PTR_TO_DYNPTR to helpers that don't set MEM_RDONLY. In
both cases such helpers won't be setting that flag.
The next patch will add a couple of selftest cases to make sure this
doesn't break.
Fixes: 205715673844 ("bpf: Add bpf_user_ringbuf_drain() helper")
Acked-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221207204141.308952-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
libbpf
This is the official home of the libbpf library.
Please use this Github repository for building and packaging libbpf and when using it in your projects through Git submodule.
Libbpf authoritative source code is developed as part of bpf-next Linux source
tree under
tools/lib/bpf subdirectory and is periodically synced to Github. As such, all the
libbpf changes should be sent to BPF mailing list,
please don't open PRs here unless you are changing Github-specific parts of libbpf
(e.g., Github-specific Makefile).
Libbpf and general BPF usage questions
Libbpf documentation can be found here. It's an ongoing effort and has ways to go, but please take a look and consider contributing as well.
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.
See also "BPF CO-RE reference guide" for the coverage of practical aspects of building BPF CO-RE applications and "BPF CO-RE" for general introduction into BPF portability issues and BPF CO-RE origins.
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.
Building libbpf
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
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)
- Manjaro (from kernel 5.4 if compiled after 2021-06-18)
- 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:
pahole1.16+ tool (part ofdwarvespackage), which performs DWARF to BTF conversion;- kernel built with
CONFIG_DEBUG_INFO_BTF=yoption; - you can check if your kernel has BTF built-in by looking for
/sys/kernel/btf/vmlinuxfile:
$ 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)
- Alpine 3.13+
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:
- BPF CO-RE reference guide
- BPF Portability and CO-RE
- HOWTO: BCC to libbpf conversion
- libbpf-tools in BCC repo contain lots of real-world tools converted from BCC to BPF CO-RE. Consider converting some more to both contribute to the BPF community and gain some more experience with it.
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 GitHub Actions.
- Static code analysis via LGTM and Coverity.
Package dependencies of libbpf, package names may vary across distros:
- zlib
- libelf
bpf-next to Github sync
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