diff mbox series

[bpf-next,v1,1/2] bpf: Transfer RCU lock state between subprog calls

Message ID 20240204230231.1013964-2-memxor@gmail.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Transfer RCU lock state across subprog calls | expand

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Commit Message

Kumar Kartikeya Dwivedi Feb. 4, 2024, 11:02 p.m. UTC
Allow transferring an imbalanced RCU lock state between subprog calls
during verification. This allows patterns where a subprog call returns
with an RCU lock held, or a subprog call releases an RCU lock held by
the caller. Currently, the verifier would end up complaining if the RCU
lock is not released when processing an exit from a subprog, which is
non-ideal if its execution is supposed to be enclosed in an RCU read
section of the caller.

Instead, simply only check whether we are processing exit for frame#0
and do not complain on an active RCU lock otherwise. We only need to
update the check when processing BPF_EXIT insn, as copy_verifier_state
is already set up to do the right thing.

Suggested-by: David Vernet <void@manifault.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Yafang Shao Feb. 5, 2024, 2:50 a.m. UTC | #1
On Mon, Feb 5, 2024 at 7:02 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>
> Allow transferring an imbalanced RCU lock state between subprog calls
> during verification. This allows patterns where a subprog call returns
> with an RCU lock held, or a subprog call releases an RCU lock held by
> the caller. Currently, the verifier would end up complaining if the RCU
> lock is not released when processing an exit from a subprog, which is
> non-ideal if its execution is supposed to be enclosed in an RCU read
> section of the caller.
>
> Instead, simply only check whether we are processing exit for frame#0
> and do not complain on an active RCU lock otherwise. We only need to
> update the check when processing BPF_EXIT insn, as copy_verifier_state
> is already set up to do the right thing.
>
> Suggested-by: David Vernet <void@manifault.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Tested-by: Yafang Shao <laoar.shao@gmail.com>

> ---
>  kernel/bpf/verifier.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 64fa188d00ad..993712b9996b 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17698,8 +17698,7 @@ static int do_check(struct bpf_verifier_env *env)
>                                         return -EINVAL;
>                                 }
>
> -                               if (env->cur_state->active_rcu_lock &&
> -                                   !in_rbtree_lock_required_cb(env)) {
> +                               if (env->cur_state->active_rcu_lock && !env->cur_state->curframe) {
>                                         verbose(env, "bpf_rcu_read_unlock is missing\n");
>                                         return -EINVAL;
>                                 }
> --
> 2.40.1
>
>
Yonghong Song Feb. 5, 2024, 3:12 a.m. UTC | #2
On 2/4/24 3:02 PM, Kumar Kartikeya Dwivedi wrote:
> Allow transferring an imbalanced RCU lock state between subprog calls
> during verification. This allows patterns where a subprog call returns
> with an RCU lock held, or a subprog call releases an RCU lock held by
> the caller. Currently, the verifier would end up complaining if the RCU
> lock is not released when processing an exit from a subprog, which is
> non-ideal if its execution is supposed to be enclosed in an RCU read
> section of the caller.
>
> Instead, simply only check whether we are processing exit for frame#0
> and do not complain on an active RCU lock otherwise. We only need to
> update the check when processing BPF_EXIT insn, as copy_verifier_state
> is already set up to do the right thing.
>
> Suggested-by: David Vernet <void@manifault.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 64fa188d00ad..993712b9996b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17698,8 +17698,7 @@  static int do_check(struct bpf_verifier_env *env)
 					return -EINVAL;
 				}
 
-				if (env->cur_state->active_rcu_lock &&
-				    !in_rbtree_lock_required_cb(env)) {
+				if (env->cur_state->active_rcu_lock && !env->cur_state->curframe) {
 					verbose(env, "bpf_rcu_read_unlock is missing\n");
 					return -EINVAL;
 				}