Currently, a set of core BPF kfuncs (e.g. bpf_task_*, bpf_cgroup_*, bpf_cpumask_*, etc) cannot be invoked from BPF_PROG_TYPE_SYSCALL programs. The whitelist approach taken for enabling kfuncs makes sense: it not safe to call these kfuncs from every program type. For example, it may not be safe to call bpf_task_acquire() in an fentry to free_task(). BPF_PROG_TYPE_SYSCALL, on the other hand, is a perfectly safe program type from which to invoke these kfuncs, as it's a very controlled environment, and we should never be able to run into any of the typical problems such as recursive invoations, acquiring references on freeing kptrs, etc. Being able to invoke these kfuncs would be useful, as BPF_PROG_TYPE_SYSCALL can be invoked with BPF_PROG_RUN, and would therefore enable user space programs to synchronously call into BPF to manipulate these kptrs. --- v1: https://lore.kernel.org/all/20240404010308.334604-1-void@xxxxxxxxxxxxx/ v1 -> v2: - Create new verifier_kfunc_prog_types testcase meant to specifically validate calling core kfuncs from various program types. Remove the macros and testcases that had been added to the task, cgrp, and cpumask kfunc testcases (Andrii and Yonghong) David Vernet (2): bpf: Allow invoking kfuncs from BPF_PROG_TYPE_SYSCALL progs selftests/bpf: Verify calling core kfuncs from BPF_PROG_TYPE_SYCALL kernel/bpf/cpumask.c | 1 + kernel/bpf/helpers.c | 1 + .../prog_tests/verifier_kfunc_prog_types.c | 11 ++ .../selftests/bpf/progs/cgrp_kfunc_common.h | 2 +- .../selftests/bpf/progs/task_kfunc_common.h | 2 +- .../bpf/progs/verifier_kfunc_prog_types.c | 119 ++++++++++++++++++ 6 files changed, 134 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier_kfunc_prog_types.c create mode 100644 tools/testing/selftests/bpf/progs/verifier_kfunc_prog_types.c -- 2.44.0
