[PATCH bpf-next v7 19/24] HID: bpf: allow to change the report descriptor

Benjamin Tissoires
2022-07-21T15:39:55Z

Add a new tracepoint hid_bpf_rdesc_fixup() so we can trigger a
report descriptor 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>

---

no changes in v7

changes in v6:
- use BTF_ID to get the btf_id of hid_bpf_rdesc_fixup

changes in v5:
- adapted for new API

not in v4

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/bpf/hid_bpf_dispatch.c | 77 ++++++++++++++++++++++++++++-
drivers/hid/bpf/hid_bpf_dispatch.h | 1 +
drivers/hid/bpf/hid_bpf_jmp_table.c | 7 +++
drivers/hid/hid-core.c | 3 +-
include/linux/hid_bpf.h | 8 +++
5 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
index cc5b29eb27f1..175b76df339b 100644
--- a/drivers/hid/bpf/hid_bpf_dispatch.c
+++ b/drivers/hid/bpf/hid_bpf_dispatch.c
@@ -85,6 +85,63 @@ dispatch_hid_bpf_device_event(struct hid_device *hdev, enum hid_report_type type
}
EXPORT_SYMBOL_GPL(dispatch_hid_bpf_device_event);

+/**
+ * hid_bpf_rdesc_fixup - Called when the probe function parses the report
+ * descriptor of the HID device
+ *
+ * @ctx: The HID-BPF context
+ *
+ * @return 0 on success and keep processing; a positive value to change the
+ * incoming size buffer; a negative error code to interrupt the processing
+ * of this event
+ *
+ * Declare an %fmod_ret tracing bpf program to this function and attach this
+ * program through hid_bpf_attach_prog() to have this helper called before any
+ * parsing of the report descriptor by HID.
+ */
+/* never used by the kernel but declared so we can load and attach a tracepoint */
+__weak noinline int hid_bpf_rdesc_fixup(struct hid_bpf_ctx *ctx)
+{
+ return 0;
+}
+ALLOW_ERROR_INJECTION(hid_bpf_rdesc_fixup, ERRNO);
+
+u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
+{
+ int ret;
+ struct hid_bpf_ctx_kern ctx_kern = {
+ .ctx = {
+ .hid = hdev,
+ .size = *size,
+ .allocated_size = HID_MAX_DESCRIPTOR_SIZE,
+ },
+ };
+
+ ctx_kern.data = kmemdup(rdesc, ctx_kern.ctx.allocated_size, GFP_KERNEL);
+ if (!ctx_kern.data)
+ goto ignore_bpf;
+
+ ret = hid_bpf_prog_run(hdev, HID_BPF_PROG_TYPE_RDESC_FIXUP, &ctx_kern);
+ if (ret < 0)
+ goto ignore_bpf;
+
+ if (ret) {
+ if (ret > ctx_kern.ctx.allocated_size)
+ goto ignore_bpf;
+
+ *size = ret;
+ }
+
+ rdesc = krealloc(ctx_kern.data, *size, GFP_KERNEL);
+
+ return rdesc;
+
+ ignore_bpf:
+ kfree(ctx_kern.data);
+ return kmemdup(rdesc, *size, GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(call_hid_bpf_rdesc_fixup);
+
/**
* hid_bpf_get_data - Get the kernel memory pointer associated with the context @ctx
*
@@ -188,6 +245,14 @@ static int hid_bpf_allocate_event_data(struct hid_device *hdev)
return __hid_bpf_allocate_data(hdev, &hdev->bpf.device_data, &hdev->bpf.allocated_data);
}

+int hid_bpf_reconnect(struct hid_device *hdev)
+{
+ if (!test_and_set_bit(ffs(HID_STAT_REPROBED), &hdev->status))
+ return device_reprobe(&hdev->dev);
+
+ return 0;
+}
+
/**
* hid_bpf_attach_prog - Attach the given @prog_fd to the given HID device
*
@@ -229,7 +294,17 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
return err;
}

- return __hid_bpf_attach_prog(hdev, prog_type, prog_fd, flags);
+ err = __hid_bpf_attach_prog(hdev, prog_type, prog_fd, flags);
+ if (err)
+ return err;
+
+ if (prog_type == HID_BPF_PROG_TYPE_RDESC_FIXUP) {
+ err = hid_bpf_reconnect(hdev);
+ if (err)
+ return err;
+ }
+
+ return 0;
}

/**
diff --git a/drivers/hid/bpf/hid_bpf_dispatch.h b/drivers/hid/bpf/hid_bpf_dispatch.h
index 98c378e18b2b..1d1d5bcccbd7 100644
--- a/drivers/hid/bpf/hid_bpf_dispatch.h
+++ b/drivers/hid/bpf/hid_bpf_dispatch.h
@@ -18,6 +18,7 @@ int __hid_bpf_attach_prog(struct hid_device *hdev, enum hid_bpf_prog_type prog_t
void __hid_bpf_destroy_device(struct hid_device *hdev);
int hid_bpf_prog_run(struct hid_device *hdev, enum hid_bpf_prog_type type,
struct hid_bpf_ctx_kern *ctx_kern);
+int hid_bpf_reconnect(struct hid_device *hdev);

struct bpf_prog;

diff --git a/drivers/hid/bpf/hid_bpf_jmp_table.c b/drivers/hid/bpf/hid_bpf_jmp_table.c
index 0f20deab81ff..3a5ab70d1a95 100644
--- a/drivers/hid/bpf/hid_bpf_jmp_table.c
+++ b/drivers/hid/bpf/hid_bpf_jmp_table.c
@@ -59,12 +59,15 @@ static DECLARE_WORK(release_work, hid_bpf_release_progs);

BTF_ID_LIST(hid_bpf_btf_ids)
BTF_ID(func, hid_bpf_device_event) /* HID_BPF_PROG_TYPE_DEVICE_EVENT */
+BTF_ID(func, hid_bpf_rdesc_fixup) /* HID_BPF_PROG_TYPE_RDESC_FIXUP */

static int hid_bpf_max_programs(enum hid_bpf_prog_type type)
{
switch (type) {
case HID_BPF_PROG_TYPE_DEVICE_EVENT:
return HID_BPF_MAX_PROGS_PER_DEV;
+ case HID_BPF_PROG_TYPE_RDESC_FIXUP:
+ return 1;
default:
return -EINVAL;
}
@@ -234,6 +237,10 @@ static void hid_bpf_release_progs(struct work_struct *work)
if (next->hdev == hdev && next->type == type)
next->hdev = NULL;
}
+
+ /* if type was rdesc fixup, reconnect device */
+ if (type == HID_BPF_PROG_TYPE_RDESC_FIXUP)
+ hid_bpf_reconnect(hdev);
}
}

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 356d3822f17d..42aed754123c 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1218,7 +1218,8 @@ int hid_open_report(struct hid_device *device)
return -ENODEV;
size = device->dev_rsize;

- buf = kmemdup(start, size, GFP_KERNEL);
+ /* call_hid_bpf_rdesc_fixup() ensures we work on a copy of rdesc */
+ buf = call_hid_bpf_rdesc_fixup(device, start, &size);
if (buf == NULL)
return -ENOMEM;

diff --git a/include/linux/hid_bpf.h b/include/linux/hid_bpf.h
index 9d1cc1ceb942..c2a090232c65 100644
--- a/include/linux/hid_bpf.h
+++ b/include/linux/hid_bpf.h
@@ -59,6 +59,7 @@ struct hid_bpf_ctx {

/* Following functions are tracepoints that BPF programs can attach to */
int hid_bpf_device_event(struct hid_bpf_ctx *ctx);
+int hid_bpf_rdesc_fixup(struct hid_bpf_ctx *ctx);

/* Following functions are kfunc that we export to BPF programs */
/* available everywhere in HID-BPF */
@@ -85,6 +86,7 @@ int __hid_bpf_tail_call(struct hid_bpf_ctx *ctx);
enum hid_bpf_prog_type {
HID_BPF_PROG_TYPE_UNDEF = -1,
HID_BPF_PROG_TYPE_DEVICE_EVENT, /* an event is emitted from the device */
+ HID_BPF_PROG_TYPE_RDESC_FIXUP,
HID_BPF_PROG_TYPE_MAX,
};

@@ -128,6 +130,7 @@ int hid_bpf_connect_device(struct hid_device *hdev);
void hid_bpf_disconnect_device(struct hid_device *hdev);
void hid_bpf_destroy_device(struct hid_device *hid);
void hid_bpf_device_init(struct hid_device *hid);
+u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size);
#else /* CONFIG_HID_BPF */
static inline u8 *dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
u32 *size, int interrupt) { return 0; }
@@ -135,6 +138,11 @@ static inline int hid_bpf_connect_device(struct hid_device *hdev) { return 0; }
static inline void hid_bpf_disconnect_device(struct hid_device *hdev) {}
static inline void hid_bpf_destroy_device(struct hid_device *hid) {}
static inline void hid_bpf_device_init(struct hid_device *hid) {}
+static inline u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
+{
+ return kmemdup(rdesc, *size, GFP_KERNEL);
+}
+
#endif /* CONFIG_HID_BPF */

#endif /* __HID_BPF_H */
--
2.36.1