Re: [PATCH v2 bpf-next 2/4] bpf: allow bpf_d_path in sleepable bpf_iter program
From: KP Singh <kpsingh@kernel.org>
Date: 2020-12-16 19:04:42
Also in:
bpf
On Wed, Dec 16, 2020 at 1:06 AM Song Liu [off-list ref] wrote:
quoted hunk ↗ jump to hunk
task_file and task_vma iter programs have access to file->f_path. Enable bpf_d_path to print paths of these file. bpf_iter programs are generally called in sleepable context. However, it is still necessary to diffientiate sleepable and non-sleepable bpf_iter programs: sleepable programs have access to bpf_d_path; non-sleepable programs have access to bpf_spin_lock. Signed-off-by: Song Liu <redacted> --- kernel/trace/bpf_trace.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 4be771df5549a..9e5f9b968355f 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c@@ -1191,6 +1191,11 @@ BTF_SET_END(btf_allowlist_d_path) static bool bpf_d_path_allowed(const struct bpf_prog *prog) { + if (prog->type == BPF_PROG_TYPE_TRACING && + prog->expected_attach_type == BPF_TRACE_ITER && + prog->aux->sleepable) + return true;
For the sleepable/non-sleepable we have been (until now) checking this in bpf_tracing_func_proto (or bpf_lsm_func_proto) eg. case BPF_FUNC_copy_from_user: return prog->aux->sleepable ? &bpf_copy_from_user_proto : NULL; But even beyond that, I don't think this is needed. We have originally exposed the helper to both sleepable and non-sleepable LSM and tracing programs with an allow list. For LSM the allow list is bpf_lsm_is_sleepable_hook) but that's just an initial allow list and thus causes some confusion w.r.t to sleep ability (maybe we should add a comment there). Based on the current logic, my understanding is that it's okay to use the helper in the allowed hooks in both "lsm.s/" and "lsm/" (and the same for BPF_PROG_TYPE_TRACING). We would have required sleepable only if this helper called "dput" (which can sleep).
+
if (prog->type == BPF_PROG_TYPE_LSM)
return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
--
2.24.1