Commit 9b5501d3 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Drop TRACING access to select_cpu kfuncs 



The select_cpu kfuncs - scx_bpf_select_cpu_dfl(), scx_bpf_select_cpu_and()
and __scx_bpf_select_cpu_and() - take task_rq_lock() internally. Exposing
them via scx_kfunc_set_idle to BPF_PROG_TYPE_TRACING is unsafe: arbitrary
tracing contexts (kprobes, tracepoints, fentry, LSM) may run with @p's
pi_lock state unknown.

Move them out of scx_kfunc_ids_idle into a new scx_kfunc_ids_select_cpu
set registered only for STRUCT_OPS and SYSCALL.

Extracted from a larger verifier-time kfunc context filter patch
originally written by Juntong Deng.

Original-patch-by: default avatarJuntong Deng <juntong.deng@outlook.com>
Cc: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
parent dcd47f27

kernel/sched/ext_idle.c

+21 −4
Original line number Diff line number Diff line
@@ -1469,9 +1469,6 @@ BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_IMPLICIT_ARGS | KF_RCU) 
BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_IMPLICIT_ARGS | KF_RCU)

BTF_ID_FLAGS(func, scx_bpf_pick_any_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_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_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU)

BTF_KFUNCS_END(scx_kfunc_ids_idle)



static const struct btf_kfunc_id_set scx_kfunc_set_idle = {
@@ -1479,13 +1476,33 @@ static const struct btf_kfunc_id_set scx_kfunc_set_idle = { 
	.set			= &scx_kfunc_ids_idle,

};



/*

 * The select_cpu kfuncs internally call task_rq_lock() when invoked from an

 * rq-unlocked context, and thus cannot be safely called from arbitrary tracing

 * contexts where @p's pi_lock state is unknown. Keep them out of

 * BPF_PROG_TYPE_TRACING by registering them in their own set which is exposed

 * only to STRUCT_OPS and SYSCALL programs.

 */

BTF_KFUNCS_START(scx_kfunc_ids_select_cpu)

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_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU)

BTF_KFUNCS_END(scx_kfunc_ids_select_cpu)



static const struct btf_kfunc_id_set scx_kfunc_set_select_cpu = {

	.owner			= THIS_MODULE,

	.set			= &scx_kfunc_ids_select_cpu,

};



int scx_idle_init(void)

{

	int ret;



	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_idle) ||

	      register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &scx_kfunc_set_idle) ||

	      register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_idle);

	      register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_idle) ||

	      register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_select_cpu) ||

	      register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_select_cpu);



	return ret;

}