[PATCH bpf-next v2 25/28] bpf/hid: Add a flag to add the program at the beginning of the list

Benjamin Tissoires
2022-03-04T17:35:56Z

When tracing the incoming events, if a bpf program is already loaded,
the next bpf program will see the potentially changed data.

Add a flag to BPF_LINK_CREATE that allows to chose the position of the
inserted program: at the beginning or at the end.

This way, we can have a tracing program that compare the raw event from
the device and the transformed stream from all the other bpf programs.

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

---

new in v2
---
include/uapi/linux/bpf.h | 10 ++++++++++
kernel/bpf/hid.c | 11 +++++++----
2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 417cf1c31579..23ebe5e96d69 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1123,6 +1123,16 @@ enum bpf_link_type {
*/
#define BPF_F_XDP_HAS_FRAGS (1U << 5)

+/* HID flag used in BPF_LINK_CREATE command
+ *
+ * NONE(default): The bpf program will be added at the tail of the list
+ * of existing bpf program for this type.
+ *
+ * BPF_F_INSERT_HEAD: The bpf program will be added at the beginning
+ * of the list of existing bpf program for this type..
+ */
+#define BPF_F_INSERT_HEAD (1U << 0)
+
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
* the following extensions:
*
diff --git a/kernel/bpf/hid.c b/kernel/bpf/hid.c
index b3dc1cd37a3e..141eb4169079 100644
--- a/kernel/bpf/hid.c
+++ b/kernel/bpf/hid.c
@@ -416,7 +416,7 @@ static int bpf_hid_max_progs(enum bpf_hid_attach_type type)
}

static int bpf_hid_link_attach(struct hid_device *hdev, struct bpf_link *link,
- enum bpf_hid_attach_type type)
+ enum bpf_hid_attach_type type, u32 flags)
{
struct bpf_hid_link *hid_link =
container_of(link, struct bpf_hid_link, link);
@@ -443,7 +443,10 @@ static int bpf_hid_link_attach(struct hid_device *hdev, struct bpf_link *link,
goto out_unlock;
}

- list_add_tail(&hid_link->node, &hdev->bpf.links[type]);
+ if (flags & BPF_F_INSERT_HEAD)
+ list_add(&hid_link->node, &hdev->bpf.links[type]);
+ else
+ list_add_tail(&hid_link->node, &hdev->bpf.links[type]);

fill_prog_array(hdev, type, run_array);
run_array = rcu_replace_pointer(hdev->bpf.run_array[type], run_array,
@@ -467,7 +470,7 @@ int bpf_hid_link_create(const union bpf_attr *attr, struct bpf_prog *prog)
struct hid_device *hdev;
int err;

- if (attr->link_create.flags || !hid_hooks.hdev_from_fd)
+ if ((attr->link_create.flags & ~BPF_F_INSERT_HEAD) || !hid_hooks.hdev_from_fd)
return -EINVAL;

type = attr->link_create.attach_type;
@@ -495,7 +498,7 @@ int bpf_hid_link_create(const union bpf_attr *attr, struct bpf_prog *prog)
return err;
}

- err = bpf_hid_link_attach(hdev, &hid_link->link, hid_type);
+ err = bpf_hid_link_attach(hdev, &hid_link->link, hid_type, attr->link_create.flags);
if (err) {
bpf_link_cleanup(&link_primer);
return err;
--
2.35.1