On Wed, Apr 3, 2024 at 6:03 PM David Vernet <void@xxxxxxxxxxxxx> wrote: > > 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. > > This patch therefore enables invoking the aforementioned core kfuncs > from BPF_PROG_TYPE_SYSCALL progs. > > Signed-off-by: David Vernet <void@xxxxxxxxxxxxx> > --- > kernel/bpf/cpumask.c | 1 + > kernel/bpf/helpers.c | 1 + > 2 files changed, 2 insertions(+) > Makes sense, but see my comments on patch #2. Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c > index dad0fb1c8e87..33c473d676a5 100644 > --- a/kernel/bpf/cpumask.c > +++ b/kernel/bpf/cpumask.c > @@ -474,6 +474,7 @@ static int __init cpumask_kfunc_init(void) > ret = bpf_mem_alloc_init(&bpf_cpumask_ma, sizeof(struct bpf_cpumask), false); > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &cpumask_kfunc_set); > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &cpumask_kfunc_set); > + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &cpumask_kfunc_set); > return ret ?: register_btf_id_dtor_kfuncs(cpumask_dtors, > ARRAY_SIZE(cpumask_dtors), > THIS_MODULE); > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index d9e7aca8ae9e..8cde717137bd 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -2653,6 +2653,7 @@ static int __init kfunc_init(void) > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &generic_kfunc_set); > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &generic_kfunc_set); > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &generic_kfunc_set); > + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &generic_kfunc_set); > ret = ret ?: register_btf_id_dtor_kfuncs(generic_dtors, > ARRAY_SIZE(generic_dtors), > THIS_MODULE); > -- > 2.44.0 >
