On Fri, Jun 21, 2024 at 1:56 AM Benjamin Tissoires <bentiss@xxxxxxxxxx> wrote:
>
> Same story than hid_hw_raw_requests:
>
> This allows to intercept and prevent or change the behavior of
> hid_hw_output_report() 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_hw_output_report(), 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@xxxxxxxxxx>
>
> ---
>
> Here checkpatch complains about:
> WARNING: use of RCU tasks trace is incorrect outside BPF or core RCU code
>
> However, we are jumping in BPF code, so I think this is correct, but I'd
> like to have the opinion on the BPF folks.
> ---
> drivers/hid/bpf/hid_bpf_dispatch.c | 37 ++++++++++++++++++++++++++++++++----
> drivers/hid/bpf/hid_bpf_struct_ops.c | 1 +
> drivers/hid/hid-core.c | 10 ++++++++--
> drivers/hid/hidraw.c | 2 +-
> include/linux/hid.h | 3 ++-
> include/linux/hid_bpf.h | 24 ++++++++++++++++++++++-
> 6 files changed, 68 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
> index 8d6e08b7c42f..2a29a0625a3b 100644
> --- a/drivers/hid/bpf/hid_bpf_dispatch.c
> +++ b/drivers/hid/bpf/hid_bpf_dispatch.c
> @@ -111,6 +111,38 @@ int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
> }
> EXPORT_SYMBOL_GPL(dispatch_hid_bpf_raw_requests);
>
> +int dispatch_hid_bpf_output_report(struct hid_device *hdev,
> + __u8 *buf, u32 size, __u64 source,
> + bool from_bpf)
> +{
> + struct hid_bpf_ctx_kern ctx_kern = {
> + .ctx = {
> + .hid = hdev,
> + .allocated_size = size,
> + .size = size,
> + },
> + .data = buf,
> + .from_bpf = from_bpf,
> + };
> + struct hid_bpf_ops *e;
> + int ret;
> +
> + rcu_read_lock_trace();
> + list_for_each_entry_rcu(e, &hdev->bpf.prog_list, list) {
> + if (e->hid_hw_output_report) {
> + ret = e->hid_hw_output_report(&ctx_kern.ctx, source);
> + if (ret)
> + goto out;
> + }
> + }
> + ret = 0;
> +
> +out:
> + rcu_read_unlock_trace();
same question.
What protects prog_list ?
list_for_each_entry_rcu() should be used within RCU CS
if elements of that list are freed via call_rcu().
rcu_read_lock_trace() looks wrong here.
