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Date: Fri, 18 Mar 2022 14:10:00 -0700
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>, Jonathan Corbet <corbet@....net>,
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,
Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 06/17] HID: allow to change the report
descriptor from an eBPF program
On Fri, Mar 18, 2022 at 9:17 AM Benjamin Tissoires
<benjamin.tissoires@...hat.com> wrote:
>
> Make use of BPF_HID_ATTACH_RDESC_FIXUP so we can trigger an rdesc fixup
> in the bpf world.
>
> Whenever the program gets attached/detached, the device is reconnected
> meaning that userspace will see it disappearing and reappearing with
> the new report descriptor.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
>
> ---
>
> changes in v3:
> - ensure the ctx.size is properly bounded by allocated size
> - s/link_attached/post_link_attach/
> - removed the switch statement with only one case
>
> changes in v2:
> - split the series by bpf/libbpf/hid/selftests and samples
> ---
> drivers/hid/hid-bpf.c | 62 ++++++++++++++++++++++++++++++++++++++++++
> drivers/hid/hid-core.c | 3 +-
> include/linux/hid.h | 6 ++++
> 3 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/hid-bpf.c b/drivers/hid/hid-bpf.c
> index 5060ebcb9979..45c87ff47324 100644
> --- a/drivers/hid/hid-bpf.c
> +++ b/drivers/hid/hid-bpf.c
> @@ -50,6 +50,14 @@ static struct hid_device *hid_bpf_fd_to_hdev(int fd)
> return hdev;
> }
>
> +static int hid_reconnect(struct hid_device *hdev)
> +{
> + if (!test_and_set_bit(ffs(HID_STAT_REPROBED), &hdev->status))
> + return device_reprobe(&hdev->dev);
> +
> + return 0;
> +}
> +
> static int hid_bpf_pre_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type type)
> {
> int err = 0;
> @@ -92,6 +100,12 @@ static int hid_bpf_pre_link_attach(struct hid_device *hdev, enum bpf_hid_attach_
> return err;
> }
>
> +static void hid_bpf_post_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type type)
> +{
> + if (type == BPF_HID_ATTACH_RDESC_FIXUP)
> + hid_reconnect(hdev);
> +}
> +
> static void hid_bpf_array_detach(struct hid_device *hdev, enum bpf_hid_attach_type type)
> {
> switch (type) {
> @@ -99,6 +113,9 @@ static void hid_bpf_array_detach(struct hid_device *hdev, enum bpf_hid_attach_ty
> kfree(hdev->bpf.device_data);
> hdev->bpf.device_data = NULL;
> break;
> + case BPF_HID_ATTACH_RDESC_FIXUP:
> + hid_reconnect(hdev);
> + break;
> default:
> /* do nothing */
> break;
> @@ -116,6 +133,9 @@ static int hid_bpf_run_progs(struct hid_device *hdev, struct hid_bpf_ctx_kern *c
> case HID_BPF_DEVICE_EVENT:
> type = BPF_HID_ATTACH_DEVICE_EVENT;
> break;
> + case HID_BPF_RDESC_FIXUP:
> + type = BPF_HID_ATTACH_RDESC_FIXUP;
> + break;
> default:
> return -EINVAL;
> }
> @@ -155,11 +175,53 @@ u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *data, int *size)
> return ctx.data;
> }
>
> +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
> +{
> + int ret;
> + struct hid_bpf_ctx_kern ctx = {
> + .type = HID_BPF_RDESC_FIXUP,
> + .hdev = hdev,
> + .size = *size,
> + };
> +
> + if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_RDESC_FIXUP))
Do we need to lock bpf_hid_mutex before calling bpf_hid_link_empty()?
(or maybe we
already did?)
> + goto ignore_bpf;
> +
> + ctx.data = kmemdup(rdesc, HID_MAX_DESCRIPTOR_SIZE, GFP_KERNEL);
> + if (!ctx.data)
> + goto ignore_bpf;
> +
> + ctx.allocated_size = HID_MAX_DESCRIPTOR_SIZE;
> +
> + ret = hid_bpf_run_progs(hdev, &ctx);
> + if (ret)
> + goto ignore_bpf;
> +
> + if (ctx.size > ctx.allocated_size)
> + goto ignore_bpf;
> +
> + *size = ctx.size;
> +
> + if (*size) {
> + rdesc = krealloc(ctx.data, *size, GFP_KERNEL);
> + } else {
> + rdesc = NULL;
> + kfree(ctx.data);
> + }
> +
> + return rdesc;
> +
> + ignore_bpf:
> + kfree(ctx.data);
> + return kmemdup(rdesc, *size, GFP_KERNEL);
> +}
> +
> int __init hid_bpf_module_init(void)
> {
> struct bpf_hid_hooks hooks = {
> .hdev_from_fd = hid_bpf_fd_to_hdev,
> .pre_link_attach = hid_bpf_pre_link_attach,
> + .post_link_attach = hid_bpf_post_link_attach,
> .array_detach = hid_bpf_array_detach,
> };
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 937fab7eb9c6..3182c39db006 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -1213,7 +1213,8 @@ int hid_open_report(struct hid_device *device)
> return -ENODEV;
> size = device->dev_rsize;
>
> - buf = kmemdup(start, size, GFP_KERNEL);
> + /* hid_bpf_report_fixup() ensures we work on a copy of rdesc */
> + buf = hid_bpf_report_fixup(device, start, &size);
> if (buf == NULL)
> return -ENOMEM;
>
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 8fd79011f461..66d949d10b78 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -1213,10 +1213,16 @@ do { \
>
> #ifdef CONFIG_BPF
> u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size);
> +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size);
> int hid_bpf_module_init(void);
> void hid_bpf_module_exit(void);
> #else
> static inline u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size) { return rd; }
> +static inline u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc,
> + unsigned int *size)
> +{
> + return kmemdup(rdesc, *size, GFP_KERNEL);
> +}
> static inline int hid_bpf_module_init(void) { return 0; }
> static inline void hid_bpf_module_exit(void) {}
> #endif
> --
> 2.35.1
>
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