From e0556a92855e49360c95f074c47d70747640a41f Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Tue, 11 Mar 2025 08:51:19 +0900 Subject: [PATCH] bpf: Tighten tail call checks for lingering locks, RCU, preempt_disable BugLink: https://bugs.launchpad.net/bugs/2101915 [ Upstream commit 46f7ed32f7a873d6675ea72e1d6317df41a55f81 ] There are three situations when a program logically exits and transfers control to the kernel or another program: bpf_throw, BPF_EXIT, and tail calls. The former two check for any lingering locks and references, but tail calls currently do not. Expand the checks to check for spin locks, RCU read sections and preempt disabled sections. Spin locks are indirectly preventing tail calls as function calls are disallowed, but the checks for preemption and RCU are more relaxed, hence ensure tail calls are prevented in their presence. Fixes: 9bb00b2895cb ("bpf: Add kfunc bpf_rcu_read_lock/unlock()") Fixes: fc7566ad0a82 ("bpf: Introduce bpf_preempt_[disable,enable] kfuncs") Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241103225940.1408302-2-memxor@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin [koichiroden: dropped the check for preempt-disabled section due to the missing commit: fc7566ad0a82 ("bpf: Introduce bpf_preempt_[disable,enable] kfuncs")] Signed-off-by: Koichiro Den Signed-off-by: Stefan Bader --- kernel/bpf/verifier.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f6e971642221..30c082c271c7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10275,11 +10275,21 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn switch (func_id) { case BPF_FUNC_tail_call: + if (env->cur_state->active_lock.ptr) { + verbose(env, "tail_call cannot be used inside bpf_spin_lock-ed region\n"); + return -EINVAL; + } + err = check_reference_leak(env, false); if (err) { verbose(env, "tail_call would lead to reference leak\n"); return err; } + + if (env->cur_state->active_rcu_lock) { + verbose(env, "tail_call cannot be used inside bpf_rcu_read_lock-ed region\n"); + return -EINVAL; + } break; case BPF_FUNC_get_local_storage: /* check that flags argument in get_local_storage(map, flags) is 0,