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bpf: Account for preempt and IRQ state in RCU protection

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Disabling preemption or local IRQs keeps the current CPU in an RCU
read-side critical section, but in_rcu_cs() does not account for either
state. The verifier therefore rejects safe kptr accesses and invalidates
pointers when another RCU source ends.

Include preemption-disabled and IRQ-disabled state in in_rcu_cs().
Invalidate RCU-protected pointers on RCU unlock, preempt enable, or IRQ
restore only after the final protection ends.

Signed-off-by: Ning Ding <dingning04@gmail.com>
Link: https://lore.kernel.org/bpf/20260805233940.3966981-2-dingning04@gmail.com
[ kkd: Simplify was_in_rcu_cs on spin unlock and adjust the selftest. ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Ning Ding 2026-08-05 16:39:33 -07:00 committed by Kumar Kartikeya Dwivedi
parent 7d008cde75
commit d65739bf93
2 changed files with 16 additions and 6 deletions
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14
kernel/bpf/verifier.c
View File

@ -4452,7 +4452,9 @@ static bool in_sleepable(struct bpf_verifier_env *env)
static bool in_rcu_cs(struct bpf_verifier_env *env)
{
return env->cur_state->active_rcu_locks ||
env->cur_state->active_preempt_locks ||
env->cur_state->active_locks ||
env->cur_state->active_irq_id ||
!in_sleepable(env);
}
@ -7166,7 +7168,6 @@ static int process_spin_lock(struct bpf_verifier_env *env, struct bpf_reg_state
return err;
}
} else {
bool was_in_rcu_cs;
void *ptr;
int type;
@ -7194,12 +7195,11 @@ static int process_spin_lock(struct bpf_verifier_env *env, struct bpf_reg_state
verbose(env, "%s_unlock cannot be out of order\n", lock_str);
return -EINVAL;
}
was_in_rcu_cs = in_rcu_cs(env);
if (release_lock_state(cur, type, reg->id, ptr)) {
verbose(env, "%s_unlock of different lock\n", lock_str);
return -EINVAL;
}
if (was_in_rcu_cs && !in_rcu_cs(env))
if (!in_rcu_cs(env))
invalidate_rcu_protected_refs(env);
invalidate_non_owning_refs(env);
@ -11663,6 +11663,9 @@ static int process_irq_flag(struct bpf_verifier_env *env, struct bpf_reg_state *
err = unmark_stack_slot_irq_flag(env, reg, kfunc_class);
if (err)
return err;
if (!in_rcu_cs(env))
invalidate_rcu_protected_refs(env);
}
return 0;
}
@ -13159,7 +13162,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
verbose(env, "unmatched rcu read unlock (kernel function %s)\n", func_name);
return -EINVAL;
}
if (--env->cur_state->active_rcu_locks == 0)
env->cur_state->active_rcu_locks--;
if (!in_rcu_cs(env))
invalidate_rcu_protected_refs(env);
} else if (preempt_disable) {
env->cur_state->active_preempt_locks++;
@ -13169,6 +13173,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
return -EINVAL;
}
env->cur_state->active_preempt_locks--;
if (!in_rcu_cs(env))
invalidate_rcu_protected_refs(env);
}
if (sleepable && !in_sleepable_context(env)) {

8
tools/testing/selftests/bpf/progs/cpumask_failure.c
View File

@ -116,9 +116,9 @@ int BPF_PROG(test_cpumask_null, struct task_struct *task, u64 clone_flags)
return 0;
}
SEC("tp_btf/task_newtask")
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
__failure __msg("R2 must be a rcu pointer")
int BPF_PROG(test_global_mask_out_of_rcu, struct task_struct *task, u64 clone_flags)
int BPF_PROG(test_global_mask_out_of_rcu)
{
struct bpf_cpumask *local, *prev;
@ -133,6 +133,10 @@ int BPF_PROG(test_global_mask_out_of_rcu, struct task_struct *task, u64 clone_fl
return 0;
}
/*
* Use a sleepable program so explicit RCU is the only source of RCU
* protection.
*/
bpf_rcu_read_lock();
local = global_mask;
if (!local) {