linux-kernel - Re: [PATCH bpf-next v2 15/28] bpf/hid: add new BPF type to trigger commands from userspace

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Date:   Thu, 10 Mar 2022 16:46:18 -0800
From:   Song Liu <song@...nel.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 15/28] bpf/hid: add new BPF type to trigger
 commands from userspace

On Fri, Mar 4, 2022 at 9:33 AM Benjamin Tissoires
<benjamin.tissoires@...hat.com> wrote:
>
> Given that we can not call bpf_hid_raw_request() from within an IRQ,
> userspace needs to have a way to communicate with the device when
> it needs.
>
> Implement a new type that the caller can run at will without being in
> an IRQ context.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
>
> ---
[...]

> +       if (user_size_out && data_out) {
> +               user_size_out = min3(user_size_out, (u32)ctx->size, (u32)ctx->allocated_size);
> +
> +               if (copy_to_user(data_out, ctx->data, user_size_out)) {
> +                       ret = -EFAULT;
> +                       goto unlock;
> +               }
> +
> +               if (copy_to_user(&uattr->test.data_size_out,
> +                                &user_size_out,
> +                                sizeof(user_size_out))) {
> +                       ret = -EFAULT;
> +                       goto unlock;
> +               }
> +       }
> +
> +       if (copy_to_user(&uattr->test.retval, &ctx->u.user.retval, sizeof(ctx->u.user.retval))) {
> +               ret = -EFAULT;
> +               goto unlock;

nit: this goto is not really needed.

> +       }
> +
> +unlock:
> +       kfree(ctx);
> +
> +       mutex_unlock(&bpf_hid_mutex);
> +       return ret;
> +}
[...]