[RFCv2 0/9] bpf: Add d_path helper

Jiri Olsa
2020-05-06T13:30:03Z

hi,
adding d_path helper to return full path for 'path' object.

I originally added and used 'file_path' helper, which did the same,
but used 'struct file' object. Then realized that file_path is just
a wrapper for d_path, so we'd cover more calling sites if we add
d_path helper and allowed resolving BTF object within another object,
so we could call d_path also with file pointer, like:

bpf_d_path(&file->f_path, buf, size);

This feature is mainly to be able to add dpath (filepath originally)
function to bpftrace, which seems to work nicely now, like:

# bpftrace -e 'kfunc:vfs_open { printf("%s\n", dpath(args->path)); }'

RFC v2 changes:

- added whitelist support, d_path helper is allowed only for
list of functions, the whitelist checking works as follows:

- helper's whitelist is defined as list of functions in file:
kernel/bpf/helpers-whitelist/helper
- at vmlinux linking time, the bpfwl tool reads the whitelist
and translates functions into BTF IDs, which are then compiled
as following data section into vmlinux object:

.BTF_whitelist
BTF_whitelist_<helper1>
BTF_whitelist_<helper2>
BTF_whitelist_<helper3>

Each BTF_whitelist_<helperX> data is a sorted array of BTF ids.
- new 'allowed' function is added to 'struct bpf_func_proto',
which is used by verifier code to check (if defined) on whether
the helper is called from allowed function (from whitelist).

Currently it's needed and implemented only for d_path helper,
but it's easy to add support for another helper.

- I don't change the btf_id value in check_func_arg as suggested by Alexei
- added new test_verifier test

Also available at:
https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
bpf/d_path

thoughts? thanks,
jirka

---
Jiri Olsa (9):
bpf: Add d_path helper
bpf: Add d_path whitelist
bpf: Add bpfwl tool to construct bpf whitelists
bpf: Allow nested BTF object to be refferenced by BTF object + offset
bpf: Add support to check on BTF id whitelist for d_path helper
bpf: Compile bpfwl tool at kernel compilation start
bpf: Compile the BTF id whitelist data in vmlinux
selftests/bpf: Add test for d_path helper
selftests/bpf: Add verifier test for d_path helper

Makefile | 24 +++++++--
include/asm-generic/vmlinux.lds.h | 5 ++
include/linux/bpf.h | 4 ++
include/uapi/linux/bpf.h | 14 +++++-
kernel/bpf/btf.c | 69 +++++++++++++++++++++++++
kernel/bpf/helpers-whitelist/d_path | 8 +++
kernel/bpf/verifier.c | 37 ++++++++++----
kernel/trace/bpf_trace.c | 54 ++++++++++++++++++++
scripts/bpf_helpers_doc.py | 2 +
scripts/link-vmlinux.sh | 20 ++++++--
tools/Makefile | 3 ++
tools/bpf/Makefile | 5 +-
tools/bpf/bpfwl/Build | 11 ++++
tools/bpf/bpfwl/Makefile | 60 ++++++++++++++++++++++
tools/bpf/bpfwl/bpfwl.c | 285 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 14 +++++-
tools/testing/selftests/bpf/prog_tests/d_path.c | 196 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
tools/testing/selftests/bpf/progs/test_d_path.c | 71 ++++++++++++++++++++++++++
tools/testing/selftests/bpf/test_verifier.c | 13 ++++-
tools/testing/selftests/bpf/verifier/d_path.c | 37 ++++++++++++++
20 files changed, 908 insertions(+), 24 deletions(-)
create mode 100644 kernel/bpf/helpers-whitelist/d_path
create mode 100644 tools/bpf/bpfwl/Build
create mode 100644 tools/bpf/bpfwl/Makefile
create mode 100644 tools/bpf/bpfwl/bpfwl.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/d_path.c
create mode 100644 tools/testing/selftests/bpf/progs/test_d_path.c
create mode 100644 tools/testing/selftests/bpf/verifier/d_path.c