On 2024/12/19 16:41, Alexei Starovoitov wrote:
On Tue, Dec 17, 2024 at 3:45 PM Juntong Deng <juntong.deng@xxxxxxxxxxx> wrote:-static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id) -{ - if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) || - prog->type == BPF_PROG_TYPE_LSM) - return 0; - return -EACCES; -} - static const struct btf_kfunc_id_set bpf_fs_kfunc_set = { .owner = THIS_MODULE, .set = &bpf_fs_kfunc_set_ids, - .filter = bpf_fs_kfuncs_filter, }; static int __init bpf_fs_kfuncs_init(void) { - return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set); + int ret; + + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set); + return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_fs_kfunc_set); } late_initcall(bpf_fs_kfuncs_init); diff --git a/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c index d6d3f4fcb24c..5aab75fd2fa5 100644 --- a/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c +++ b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c @@ -148,14 +148,4 @@ int BPF_PROG(path_d_path_kfunc_invalid_buf_sz, struct file *file) return 0; } -SEC("fentry/vfs_open") -__failure __msg("calling kernel function bpf_path_d_path is not allowed")This is incorrect. You have to keep bpf_fs_kfuncs_filter() and prog->type == BPF_PROG_TYPE_LSM check because bpf_prog_type_to_kfunc_hook() aliases LSM and fentry into BTF_KFUNC_HOOK_TRACING category. It's been an annoying quirk. We're figuring out details for significant refactoring of register_btf_kfunc_id_set() and the whole registration process. Maybe you would be interested in working on it? The main goal is to get rid of run-time mask check in SCX_CALL_OP() and make it static by the verifier. To make that happen scx_kf_mask flags would need to become KF_* flags while each struct-ops callback will specify the expected mask. Then at struct-ops prog attach time the verifier will see the expected mask and can check that all kfuncs calls of this particular program satisfy the mask. Then all of the runtime overhead of current->scx.kf_mask and scx_kf_allowed() will go away.
Thanks for pointing this out. Yes, I am interested in working on it. I will try to solve this problem in a separate patch series. The following are my thoughts: Should we really use KF_* to do this? I think KF_* is currently more like declaring that a kfunc has some kind of attribute, e.g. KF_TRUSTED_ARGS means that the kfunc only accepts trusted arguments, rather than being used to categorise kfuncs. It is not sustainable to restrict the kfuncs that can be used based on program types, which are coarse-grained. This problem will get worse as kfuncs increase. In my opinion, managing the kfuncs available to bpf programs should be implemented as capabilities. Capabilities are a mature permission model. We can treat a set of kfuncs as a capability (like the various current kfunc_sets, but the current kfunc_sets did not carefully divide permissions). We should use separate BPF_CAP_XXX flags to manage these capabilities. For example, SCX may define BPF_CAP_SCX_DISPATCH. For program types, we should divide them into two levels, types and subtypes. Types are used to register common capabilities and subtypes are used to register specific capabilities. The verifier can check if the used kfuncs are allowed based on the type and subtype of the bpf program. I understand that we need to maintain backward compatibility to userspace, but capabilities are internal changes in the kernel. Perhaps we can make the current program types as subtypes and add 'types' that are only used internally, and more subtypes (program types) can be added in the future.
