mbox series

[v5,bpf-next,00/14] Support BTF-powered BPF tracing programs for kernel modules

Message ID 20201203035204.1411380-1-andrii@kernel.org
Headers show
Series Support BTF-powered BPF tracing programs for kernel modules | expand

Message

Andrii Nakryiko Dec. 3, 2020, 3:51 a.m. UTC 
This patch sets extends kernel and libbpf with support for attaching
BTF-powered raw tracepoint (tp_btf) and tracing (fentry/fexit/fmod_ret/lsm)
BPF programs to BPF hooks defined in kernel modules. As part of that, libbpf
now supports performing CO-RE relocations against types in kernel module BTFs,
in addition to existing vmlinux BTF support.

Kernel UAPI for BPF_PROG_LOAD now allows to specify kernel module (or vmlinux)
BTF object FD in attach_btf_obj_fd field, aliased to attach_prog_fd. This is
used to identify which BTF object needs to be used for finding BTF type by
provided attach_btf_id.

This patch set also sets up a convenient and fully-controlled custom kernel
module (called "bpf_testmod"), that is a predictable playground for all the
BPF selftests, that rely on module BTFs. Currently pahole doesn't generate
BTF_KIND_FUNC info for ftrace-able static functions in kernel modules, so
expose traced function in bpf_sidecar.ko. Once pahole is enhanced, we can go
back to static function.

Comments

John Fastabend Dec. 3, 2020, 4:36 a.m. UTC | #1 
Andrii Nakryiko wrote:
> __module_address() needs to be called with preemption disabled or with
> module_mutex taken. preempt_disable() is enough for read-only uses, which is
> what this fix does. Also, module_put() does internal check for NULL, so drop
> it as well.
> 
> Fixes: a38d1107f937 ("bpf: support raw tracepoints in modules")
> Acked-by: Martin KaFai Lau <kafai@fb.com>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---

Acked-by: John Fastabend <john.fastabend@gmail.com>