[PATCH bpf-next v2 08/28] HID: allow to change the report descriptor from an eBPF program

Benjamin Tissoires
2022-03-04T17:31:57Z

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@redhat.com>

---

changes in v2:
- split the series by bpf/libbpf/hid/selftests and samples
---
drivers/hid/hid-bpf.c | 60 ++++++++++++++++++++++++++++++++++++++++++
drivers/hid/hid-core.c | 3 ++-
include/linux/hid.h | 6 +++++
3 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-bpf.c b/drivers/hid/hid-bpf.c
index 8120e598de9f..510e24f4307c 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_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type type)
{
int err = 0;
@@ -71,6 +79,17 @@ static int hid_bpf_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type
return err;
}

+static void hid_bpf_link_attached(struct hid_device *hdev, enum bpf_hid_attach_type type)
+{
+ switch (type) {
+ case BPF_HID_ATTACH_RDESC_FIXUP:
+ hid_reconnect(hdev);
+ break;
+ default:
+ /* do nothing */
+ }
+}
+
static void hid_bpf_array_detached(struct hid_device *hdev, enum bpf_hid_attach_type type)
{
switch (type) {
@@ -78,6 +97,9 @@ static void hid_bpf_array_detached(struct hid_device *hdev, enum bpf_hid_attach_
kfree(hdev->bpf.ctx);
hdev->bpf.ctx = NULL;
break;
+ case BPF_HID_ATTACH_RDESC_FIXUP:
+ hid_reconnect(hdev);
+ break;
default:
/* do nothing */
}
@@ -98,6 +120,9 @@ static int hid_bpf_run_progs(struct hid_device *hdev, enum bpf_hid_attach_type t
case BPF_HID_ATTACH_DEVICE_EVENT:
event = HID_BPF_DEVICE_EVENT;
break;
+ case BPF_HID_ATTACH_RDESC_FIXUP:
+ event = HID_BPF_RDESC_FIXUP;
+ break;
default:
return -EINVAL;
}
@@ -138,11 +163,46 @@ u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *data, int *size)
return hdev->bpf.ctx->data;
}

+u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
+{
+ struct hid_bpf_ctx *ctx = NULL;
+ int ret;
+
+ if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_RDESC_FIXUP))
+ goto ignore_bpf;
+
+ ctx = bpf_hid_allocate_ctx(hdev, HID_MAX_DESCRIPTOR_SIZE);
+ if (IS_ERR(ctx))
+ goto ignore_bpf;
+
+ ret = hid_bpf_run_progs(hdev, BPF_HID_ATTACH_RDESC_FIXUP, ctx, rdesc, *size);
+ if (ret)
+ goto ignore_bpf;
+
+ *size = ctx->size;
+
+ if (!*size) {
+ rdesc = NULL;
+ goto unlock;
+ }
+
+ rdesc = kmemdup(ctx->data, *size, GFP_KERNEL);
+
+ unlock:
+ kfree(ctx);
+ return rdesc;
+
+ ignore_bpf:
+ kfree(ctx);
+ 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,
.link_attach = hid_bpf_link_attach,
+ .link_attached = hid_bpf_link_attached,
.array_detached = hid_bpf_array_detached,
};

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index a80bffe6ce4a..0eb8189faaee 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