sched_ext: Forbid cpu-form kfuncs from cid-form schedulers

cid and cpu are both small s32s, trivially confused when a cid-form
scheduler calls a cpu-keyed kfunc. Reject cid-form programs that
reference any kfunc in the new scx_kfunc_ids_cpu_only at verifier load
time.

The reverse direction is intentionally permissive: cpu-form schedulers
can freely call cid-form kfuncs to ease a gradual cpumask -> cid
migration.

The check sits in scx_kfunc_context_filter() right after the SCX
struct_ops gate and before the any/idle allow and per-op allow-list
checks, so it catches cpu-only kfuncs regardless of which set they
belong to (any, idle, or select_cpu).

v2: Sync per-entry kfunc flags with their primary declarations (Zhao).
    pahole intersects flags across BTF_ID_FLAGS() occurrences, so
    omitting them drops the flags globally.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Reviewed-by: Changwoo Min <changwoo@igalia.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 79565fabd9b495cdf38cf496ac129b103e6a3639..65a00c9796915d773778ecabae6e128a9a8b66ff 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -10121,6 +10121,47 @@ static const struct btf_kfunc_id_set scx_kfunc_set_any = {
        .filter                 = scx_kfunc_context_filter,
 };
 
+/*
+ * cpu-form kfuncs that are forbidden from cid-form schedulers
+ * (bpf_sched_ext_ops_cid). Programs targeting the cid struct_ops type must
+ * use the cid-form alternative (cid/cmask kfuncs).
+ *
+ * Membership overlaps with scx_kfunc_ids_{any,idle,select_cpu}; the filter
+ * tests this set independently and rejects matches before the per-op
+ * allow-list check runs.
+ *
+ * pahole/resolve_btfids scans every BTF_ID_FLAGS() at build time and
+ * intersects flags across duplicate entries, so each entry must carry the
+ * same flags as the kfunc's primary declaration; otherwise the flags get
+ * dropped globally.
+ */
+BTF_KFUNCS_START(scx_kfunc_ids_cpu_only)
+BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
+BTF_ID_FLAGS(func, scx_bpf_cpu_node, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE)
+BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask, KF_IMPLICIT_ARGS | KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask_node, KF_IMPLICIT_ARGS | KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask, KF_IMPLICIT_ARGS | KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask_node, KF_IMPLICIT_ARGS | KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask, KF_RELEASE)
+BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node, KF_IMPLICIT_ARGS | KF_RCU)
+BTF_KFUNCS_END(scx_kfunc_ids_cpu_only)
+
 /*
  * Per-op kfunc allow flags. Each bit corresponds to a context-sensitive kfunc
  * group; an op may permit zero or more groups, with the union expressed in
@@ -10184,6 +10225,7 @@ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id)
        bool in_cpu_release = btf_id_set8_contains(&scx_kfunc_ids_cpu_release, kfunc_id);
        bool in_idle = btf_id_set8_contains(&scx_kfunc_ids_idle, kfunc_id);
        bool in_any = btf_id_set8_contains(&scx_kfunc_ids_any, kfunc_id);
+       bool in_cpu_only = btf_id_set8_contains(&scx_kfunc_ids_cpu_only, kfunc_id);
        u32 moff, flags;
 
        /* Not an SCX kfunc - allow. */
@@ -10221,6 +10263,15 @@ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id)
            prog->aux->st_ops != &bpf_sched_ext_ops_cid)
                return -EACCES;
 
+       /*
+        * cid-form schedulers must use cid/cmask kfuncs. cid and cpu are both
+        * small s32s and trivially confused, so cpu-only kfuncs are rejected at
+        * load time. The reverse (cpu-form calling cid-form kfuncs) is
+        * intentionally permissive to ease gradual cpumask -> cid migration.
+        */
+       if (prog->aux->st_ops == &bpf_sched_ext_ops_cid && in_cpu_only)
+               return -EACCES;
+
        /* SCX struct_ops: check the per-op allow list. */
        if (in_any || in_idle)
                return 0;