linux-kernel - Re: [PATCH HID v2 04/13] HID: bpf: add HID-BPF hooks for hid_hw_raw

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Date: Wed, 26 Jun 2024 09:29:57 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Benjamin Tissoires <bentiss@...nel.org>
Cc: Jiri Kosina <jikos@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	Jonathan Corbet <corbet@....net>, "open list:HID CORE LAYER" <linux-input@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH HID v2 04/13] HID: bpf: add HID-BPF hooks for hid_hw_raw_requests

On Wed, Jun 26, 2024 at 6:46 AM Benjamin Tissoires <bentiss@...nel.org> wrote:
>
> This allows to intercept and prevent or change the behavior of
> hid_hw_raw_request() from a bpf program.
>
> The intent is to solve a couple of use case:
> - firewalling a HID device: a firewall can monitor who opens the hidraw
>   nodes and then prevent or allow access to write operations on that
>   hidraw node.
> - change the behavior of a device and emulate a new HID feature request
>
> The hook is allowed to be run as sleepable so it can itself call
> hid_bpf_hw_request(), which allows to "convert" one feature request into
> another or even call the feature request on a different HID device on the
> same physical device.
>
> Signed-off-by: Benjamin Tissoires <bentiss@...nel.org>
>
> ---
>
> changes in v2:
> - make use of SRCU
> ---
>  drivers/hid/bpf/hid_bpf_dispatch.c   | 37 ++++++++++++++++++++++++++++++++++++
>  drivers/hid/bpf/hid_bpf_struct_ops.c |  1 +
>  drivers/hid/hid-core.c               |  6 ++++++
>  include/linux/hid_bpf.h              | 35 ++++++++++++++++++++++++++++++++++
>  4 files changed, 79 insertions(+)
>
> diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
> index c026248e3d73..ac98bab4c96d 100644
> --- a/drivers/hid/bpf/hid_bpf_dispatch.c
> +++ b/drivers/hid/bpf/hid_bpf_dispatch.c
> @@ -74,6 +74,43 @@ dispatch_hid_bpf_device_event(struct hid_device *hdev, enum hid_report_type type
>  }
>  EXPORT_SYMBOL_GPL(dispatch_hid_bpf_device_event);
>
> +int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
> +                                 unsigned char reportnum, u8 *buf,
> +                                 u32 size, enum hid_report_type rtype,
> +                                 enum hid_class_request reqtype,
> +                                 u64 source)
> +{
> +       struct hid_bpf_ctx_kern ctx_kern = {
> +               .ctx = {
> +                       .hid = hdev,
> +                       .allocated_size = size,
> +                       .size = size,
> +               },
> +               .data = buf,
> +       };
> +       struct hid_bpf_ops *e;
> +       int ret, idx;
> +
> +       if (rtype >= HID_REPORT_TYPES)
> +               return -EINVAL;
> +
> +       idx = srcu_read_lock(&hdev->bpf.srcu);
> +       list_for_each_entry_srcu(e, &hdev->bpf.prog_list, list,
> +                                srcu_read_lock_held(&hdev->bpf.srcu)) {
> +               if (e->hid_hw_request) {
> +                       ret = e->hid_hw_request(&ctx_kern.ctx, reportnum, rtype, reqtype, source);
> +                       if (ret)
> +                               goto out;
> +               }
> +       }

here and in patch 7 I would reduce indent by doing:
if (!e->hid_hw_request)
   continue;
ret = e->hid_hw_request(...);

otherwise lgtm