RFC bpf: Add buildid check support

hi,
eBPF programs loaded for kprobes are allowed to read kernel internal structures. We check the provided kernel version to ensure that the program is loaded for the proper kernel.

The problem is that the version check is not enough, because it only follows the version setup from kernel's Makefile. However, the internal kernel structures change based on the .config data, so in practise we have different kernels with same version.

The eBPF kprobe program thus then get loaded for different kernel than it's been built for, get wrong data (silently) and provide misleading output.

This patchset implements additional check in eBPF loading code on provided build ID (from kernel's elf image, .notes section GNU build ID) to ensure we load the eBPF program on correct kernel.

Also available in here (based on bpf-next/master):
https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
bpf/checksum

This patchset consists of several changes:

- adding CONFIG_BUILDID_H option that instructs the build to generate uapi header file with build ID data, that will be included by eBPF program

- adding CONFIG_BPF_BUILDID_CHECK option and new bpf_attr field to allow build ID checking when loading the eBPF program

- changing libbpf to read and pass build ID to the kernel

- several small side fixes

- example perf eBPF code in bpf-samples/bpf-stdout-example.c to show the build ID support/usage.

    # perf record -vv  -e ./bpf-samples/bpf-stdout-example.c kill 2>&1 | grep buildid
    libbpf: section(7) buildid, size 21, link 0, flags 3, type=1
    libbpf: kernel buildid of ./bpf-samples/bpf-stdout-example.c is: 6e25edeb408513184e2753bebad25d42314501a0

The buildid is provided the same way we provide kernel version, in a special "buildid" section:

    # cat ./bpf-samples/bpf-stdout-example.c
    ...
    #include <linux/buildid.h>

    char _buildid[] SEC("buildid") = LINUX_BUILDID_DATA;
    ...

where LINUX_BUILDID_DATA is defined in the generated buildid.h.

please note it's an RFC ;-) any comments and suggestions are welcome

thanks,
jirka

---
Jiri Olsa (9):
perf tools: Make read_build_id function public perf tools: Add fetch_kernel_buildid function
kbuild: Do not pass arguments to link-vmlinux.sh
kbuild: Add filechk2 function
bpf: Add CONFIG_BUILDID_H option
bpf: Add CONFIG_BPF_BUILDID_CHECK option
libbpf: Synchronize uapi bpf.h header
libbpf: Add support to attach buildid to program load perf tools: The buildid usage in example eBPF program

 Makefile                                    | 14 +++++++++++++-
 include/uapi/linux/bpf.h                    |  2 ++
 init/Kconfig                                | 12 ++++++++++++
 kernel/bpf/syscall.c                        | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 scripts/Kbuild.include                      | 24 ++++++++++++++++++++++++
 scripts/Makefile                            |  1 +
 scripts/extract-buildid.c                   | 42 ++++++++++++++++++++++++++++++++++++++++++
 tools/bpf/bpftool/Makefile                  |  5 ++++-
 tools/include/uapi/linux/bpf.h              |  3 +++
 tools/lib/bpf/bpf.c                         |  6 ++++--
 tools/lib/bpf/bpf.h                         |  5 +++--
 tools/lib/bpf/libbpf.c                      | 46 ++++++++++++++++++++++++++++++++++++++++------
 tools/perf/bpf-samples/bpf-stdout-example.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 tools/perf/tests/bpf.c                      |  9 ++++++++-
 tools/perf/util/symbol-minimal.c            | 50 ++------------------------------------------------
 tools/perf/util/util.c                      | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/util.h                      |  6 ++++++
 17 files changed, 355 insertions(+), 62 deletions(-)
 create mode 100644 scripts/extract-buildid.c
 create mode 100644 tools/perf/bpf-samples/bpf-stdout-example.c