[PATCH bpf-next v2 12/28] bpf/hid: add hid_{get|set}_data helpers

Benjamin Tissoires
2022-03-04T17:33:29Z

When we process an incoming HID report, it is common to have to account
for fields that are not aligned in the report. HID is using 2 helpers
hid_field_extract() and implement() to pick up any data at any offset
within the report.

Export those 2 helpers in BPF programs so users can also rely on them.
The second net worth advantage of those helpers is that now we can
fetch data anywhere in the report without knowing at compile time the
location of it. The boundary checks are done in hid-bpf.c, to prevent
a memory leak.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

changes in v2:
- split the patch with libbpf and HID left outside.
---
include/linux/bpf-hid.h | 4 +++
include/uapi/linux/bpf.h | 32 ++++++++++++++++++++
kernel/bpf/hid.c | 53 ++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 32 ++++++++++++++++++++
4 files changed, 121 insertions(+)

diff --git a/include/linux/bpf-hid.h b/include/linux/bpf-hid.h
index 0c5000b28b20..69bb28523ceb 100644
--- a/include/linux/bpf-hid.h
+++ b/include/linux/bpf-hid.h
@@ -93,6 +93,10 @@ struct bpf_hid_hooks {
int (*link_attach)(struct hid_device *hdev, enum bpf_hid_attach_type type);
void (*link_attached)(struct hid_device *hdev, enum bpf_hid_attach_type type);
void (*array_detached)(struct hid_device *hdev, enum bpf_hid_attach_type type);
+ int (*hid_get_data)(struct hid_device *hdev, u8 *buf, size_t buf_size,
+ u64 offset, u32 n, u8 *data, u64 data_size);
+ int (*hid_set_data)(struct hid_device *hdev, u8 *buf, size_t buf_size,
+ u64 offset, u32 n, u8 *data, u64 data_size);
};

#ifdef CONFIG_BPF
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a7a8d9cfcf24..4845a20e6f96 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5090,6 +5090,36 @@ union bpf_attr {
* Return
* 0 on success, or a negative error in case of failure. On error
* *dst* buffer is zeroed out.
+ *
+ * int bpf_hid_get_data(void *ctx, u64 offset, u32 n, u8 *data, u64 size)
+ * Description
+ * Get the data of size n (in bits) at the given offset (bits) in the
+ * ctx->event.data field and store it into data.
+ *
+ * if n is less or equal than 32, we can address with bit precision,
+ * the value in the buffer. However, data must be a pointer to a u32
+ * and size must be 4.
+ *
+ * if n is greater than 32, offset and n must be a multiple of 8
+ * and the result is working with a memcpy internally.
+ * Return
+ * The length of data copied into data. On error, a negative value
+ * is returned.
+ *
+ * int bpf_hid_set_data(void *ctx, u64 offset, u32 n, u8 *data, u64 size)
+ * Description
+ * Set the data of size n (in bits) at the given offset (bits) in the
+ * ctx->event.data field.
+ *
+ * if n is less or equal than 32, we can address with bit precision,
+ * the value in the buffer. However, data must be a pointer to a u32
+ * and size must be 4.
+ *
+ * if n is greater than 32, offset and n must be a multiple of 8
+ * and the result is working with a memcpy internally.
+ * Return
+ * The length of data copied into ctx->event.data. On error, a negative
+ * value is returned.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5284,6 +5314,8 @@ union bpf_attr {
FN(xdp_load_bytes), \
FN(xdp_store_bytes), \
FN(copy_from_user_task), \
+ FN(hid_get_data), \
+ FN(hid_set_data), \
/* */

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/hid.c b/kernel/bpf/hid.c
index 37500313e270..640e55ba66ec 100644
--- a/kernel/bpf/hid.c
+++ b/kernel/bpf/hid.c
@@ -37,10 +37,63 @@ void bpf_hid_set_hooks(struct bpf_hid_hooks *hooks)
}
EXPORT_SYMBOL_GPL(bpf_hid_set_hooks);

+BPF_CALL_5(bpf_hid_get_data, void*, ctx, u64, offset, u32, n, void*, data, u64, size)
+{
+ struct hid_bpf_ctx *bpf_ctx = ctx;
+
+ if (!hid_hooks.hid_get_data)
+ return -EOPNOTSUPP;
+
+ return hid_hooks.hid_get_data(bpf_ctx->hdev,
+ bpf_ctx->data, bpf_ctx->allocated_size,
+ offset, n,
+ data, size);
+}
+
+static const struct bpf_func_proto bpf_hid_get_data_proto = {
+ .func = bpf_hid_get_data,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_PTR_TO_MEM,
+ .arg5_type = ARG_CONST_SIZE_OR_ZERO,
+};
+
+BPF_CALL_5(bpf_hid_set_data, void*, ctx, u64, offset, u32, n, void*, data, u64, size)
+{
+ struct hid_bpf_ctx *bpf_ctx = ctx;
+
+ if (!hid_hooks.hid_set_data)
+ return -EOPNOTSUPP;
+
+ hid_hooks.hid_set_data(bpf_ctx->hdev,
+ bpf_ctx->data, bpf_ctx->allocated_size,
+ offset, n,
+ data, size);
+ return 0;
+}
+
+static const struct bpf_func_proto bpf_hid_set_data_proto = {
+ .func = bpf_hid_set_data,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_PTR_TO_MEM,
+ .arg5_type = ARG_CONST_SIZE_OR_ZERO,
+};
+
static const struct bpf_func_proto *
hid_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
{
switch (func_id) {
+ case BPF_FUNC_hid_get_data:
+ return &bpf_hid_get_data_proto;
+ case BPF_FUNC_hid_set_data:
+ return &bpf_hid_set_data_proto;
default:
return bpf_base_func_proto(func_id);
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a7a8d9cfcf24..4845a20e6f96 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5090,6 +5090,36 @@ union bpf_attr {
* Return
* 0 on success, or a negative error in case of failure. On error
* *dst* buffer is zeroed out.
+ *
+ * int bpf_hid_get_data(void *ctx, u64 offset, u32 n, u8 *data, u64 size)
+ * Description
+ * Get the data of size n (in bits) at the given offset (bits) in the
+ * ctx->event.data field and store it into data.
+ *
+ * if n is less or equal than 32, we can address with bit precision,
+ * the value in the buffer. However, data must be a pointer to a u32
+ * and size must be 4.
+ *
+ * if n is greater than 32, offset and n must be a multiple of 8
+ * and the result is working with a memcpy internally.
+ * Return
+ * The length of data copied into data. On error, a negative value
+ * is returned.
+ *
+ * int bpf_hid_set_data(void *ctx, u64 offset, u32 n, u8 *data, u64 size)
+ * Description
+ * Set the data of size n (in bits) at the given offset (bits) in the
+ * ctx->event.data field.
+ *
+ * if n is less or equal than 32, we can address with bit precision,
+ * the value in the buffer. However, data must be a pointer to a u32
+ * and size must be 4.
+ *
+ * if n is greater than 32, offset and n must be a multiple of 8
+ * and the result is working with a memcpy internally.
+ * Return
+ * The length of data copied into ctx->event.data. On error, a negative
+ * value is returned.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5284,6 +5314,8 @@ union bpf_attr {
FN(xdp_load_bytes), \
FN(xdp_store_bytes), \
FN(copy_from_user_task), \
+ FN(hid_get_data), \
+ FN(hid_set_data), \
/* */

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.35.1