1 files changed, 307 insertions, 0 deletions
diff --git a/drivers/hid/bpf/hid_bpf_struct_ops.c b/drivers/hid/bpf/hid_bpf_struct_ops.c
new file mode 100644
index 000000000000..f59cce6e437f
--- /dev/null
+++ b/drivers/hid/bpf/hid_bpf_struct_ops.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ *  HID-BPF support for Linux
+ *
+ *  Copyright (c) 2024 Benjamin Tissoires
+ */
+
+#include <linux/bitops.h>
+#include <linux/bpf_verifier.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+#include <linux/filter.h>
+#include <linux/hid.h>
+#include <linux/hid_bpf.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/stddef.h>
+#include <linux/workqueue.h>
+#include "hid_bpf_dispatch.h"
+
+static struct btf *hid_bpf_ops_btf;
+
+static int hid_bpf_ops_init(struct btf *btf)
+{
+	hid_bpf_ops_btf = btf;
+	return 0;
+}
+
+static bool hid_bpf_ops_is_valid_access(int off, int size,
+					  enum bpf_access_type type,
+					  const struct bpf_prog *prog,
+					  struct bpf_insn_access_aux *info)
+{
+	return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
+}
+
+static int hid_bpf_ops_check_member(const struct btf_type *t,
+				      const struct btf_member *member,
+				      const struct bpf_prog *prog)
+{
+	u32 moff = __btf_member_bit_offset(t, member) / 8;
+
+	switch (moff) {
+	case offsetof(struct hid_bpf_ops, hid_rdesc_fixup):
+	case offsetof(struct hid_bpf_ops, hid_hw_request):
+	case offsetof(struct hid_bpf_ops, hid_hw_output_report):
+		break;
+	default:
+		if (prog->sleepable)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+struct hid_bpf_offset_write_range {
+	const char *struct_name;
+	u32 struct_length;
+	u32 start;
+	u32 end;
+};
+
+static int hid_bpf_ops_btf_struct_access(struct bpf_verifier_log *log,
+					   const struct bpf_reg_state *reg,
+					   int off, int size)
+{
+#define WRITE_RANGE(_name, _field, _is_string)					\
+	{									\
+		.struct_name = #_name,						\
+		.struct_length = sizeof(struct _name),				\
+		.start = offsetof(struct _name, _field),			\
+		.end = offsetofend(struct _name, _field) - !!(_is_string),	\
+	}
+
+	const struct hid_bpf_offset_write_range write_ranges[] = {
+		WRITE_RANGE(hid_bpf_ctx, retval, false),
+		WRITE_RANGE(hid_device, name, true),
+		WRITE_RANGE(hid_device, uniq, true),
+		WRITE_RANGE(hid_device, phys, true),
+	};
+#undef WRITE_RANGE
+	const struct btf_type *state = NULL;
+	const struct btf_type *t;
+	const char *cur = NULL;
+	int i;
+
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+
+	for (i = 0; i < ARRAY_SIZE(write_ranges); i++) {
+		const struct hid_bpf_offset_write_range *write_range = &write_ranges[i];
+		s32 type_id;
+
+		/* we already found a writeable struct, but there is a
+		 * new one, let's break the loop.
+		 */
+		if (t == state && write_range->struct_name != cur)
+			break;
+
+		/* new struct to look for */
+		if (write_range->struct_name != cur) {
+			type_id = btf_find_by_name_kind(reg->btf, write_range->struct_name,
+							BTF_KIND_STRUCT);
+			if (type_id < 0)
+				return -EINVAL;
+
+			state = btf_type_by_id(reg->btf, type_id);
+		}
+
+		/* this is not the struct we are looking for */
+		if (t != state) {
+			cur = write_range->struct_name;
+			continue;
+		}
+
+		/* first time we see this struct, check for out of bounds */
+		if (cur != write_range->struct_name &&
+		    off + size > write_range->struct_length) {
+			bpf_log(log, "write access for struct %s at off %d with size %d\n",
+				write_range->struct_name, off, size);
+			return -EACCES;
+		}
+
+		/* now check if we are in our boundaries */
+		if (off >= write_range->start && off + size <= write_range->end)
+			return NOT_INIT;
+
+		cur = write_range->struct_name;
+	}
+
+
+	if (t != state)
+		bpf_log(log, "write access to this struct is not supported\n");
+	else
+		bpf_log(log,
+			"write access at off %d with size %d on read-only part of %s\n",
+			off, size, cur);
+
+	return -EACCES;
+}
+
+static const struct bpf_verifier_ops hid_bpf_verifier_ops = {
+	.get_func_proto = bpf_base_func_proto,
+	.is_valid_access = hid_bpf_ops_is_valid_access,
+	.btf_struct_access = hid_bpf_ops_btf_struct_access,
+};
+
+static int hid_bpf_ops_init_member(const struct btf_type *t,
+				 const struct btf_member *member,
+				 void *kdata, const void *udata)
+{
+	const struct hid_bpf_ops *uhid_bpf_ops;
+	struct hid_bpf_ops *khid_bpf_ops;
+	u32 moff;
+
+	uhid_bpf_ops = (const struct hid_bpf_ops *)udata;
+	khid_bpf_ops = (struct hid_bpf_ops *)kdata;
+
+	moff = __btf_member_bit_offset(t, member) / 8;
+
+	switch (moff) {
+	case offsetof(struct hid_bpf_ops, hid_id):
+		/* For hid_id and flags fields, this function has to copy it
+		 * and return 1 to indicate that the data has been handled by
+		 * the struct_ops type, or the verifier will reject the map if
+		 * the value of those fields is not zero.
+		 */
+		khid_bpf_ops->hid_id = uhid_bpf_ops->hid_id;
+		return 1;
+	case offsetof(struct hid_bpf_ops, flags):
+		if (uhid_bpf_ops->flags & ~BPF_F_BEFORE)
+			return -EINVAL;
+		khid_bpf_ops->flags = uhid_bpf_ops->flags;
+		return 1;
+	}
+	return 0;
+}
+
+static int hid_bpf_reg(void *kdata, struct bpf_link *link)
+{
+	struct hid_bpf_ops *ops = kdata;
+	struct hid_device *hdev;
+	int count, err = 0;
+
+	hdev = hid_get_device(ops->hid_id);
+	if (IS_ERR(hdev))
+		return PTR_ERR(hdev);
+
+	ops->hdev = hdev;
+
+	mutex_lock(&hdev->bpf.prog_list_lock);
+
+	count = list_count_nodes(&hdev->bpf.prog_list);
+	if (count >= HID_BPF_MAX_PROGS_PER_DEV) {
+		err = -E2BIG;
+		goto out_unlock;
+	}
+
+	if (ops->hid_rdesc_fixup) {
+		if (hdev->bpf.rdesc_ops) {
+			err = -EINVAL;
+			goto out_unlock;
+		}
+
+		hdev->bpf.rdesc_ops = ops;
+	}
+
+	if (ops->hid_device_event) {
+		err = hid_bpf_allocate_event_data(hdev);
+		if (err)
+			goto out_unlock;
+	}
+
+	if (ops->flags & BPF_F_BEFORE)
+		list_add_rcu(&ops->list, &hdev->bpf.prog_list);
+	else
+		list_add_tail_rcu(&ops->list, &hdev->bpf.prog_list);
+	synchronize_srcu(&hdev->bpf.srcu);
+
+out_unlock:
+	mutex_unlock(&hdev->bpf.prog_list_lock);
+
+	if (err) {
+		if (hdev->bpf.rdesc_ops == ops)
+			hdev->bpf.rdesc_ops = NULL;
+		hid_put_device(hdev);
+	} else if (ops->hid_rdesc_fixup) {
+		hid_bpf_reconnect(hdev);
+	}
+
+	return err;
+}
+
+static void hid_bpf_unreg(void *kdata, struct bpf_link *link)
+{
+	struct hid_bpf_ops *ops = kdata;
+	struct hid_device *hdev;
+	bool reconnect = false;
+
+	hdev = ops->hdev;
+
+	/* check if __hid_bpf_ops_destroy_device() has been called */
+	if (!hdev)
+		return;
+
+	mutex_lock(&hdev->bpf.prog_list_lock);
+
+	list_del_rcu(&ops->list);
+	synchronize_srcu(&hdev->bpf.srcu);
+
+	reconnect = hdev->bpf.rdesc_ops == ops;
+	if (reconnect)
+		hdev->bpf.rdesc_ops = NULL;
+
+	mutex_unlock(&hdev->bpf.prog_list_lock);
+
+	if (reconnect)
+		hid_bpf_reconnect(hdev);
+
+	hid_put_device(hdev);
+}
+
+static int __hid_bpf_device_event(struct hid_bpf_ctx *ctx, enum hid_report_type type, u64 source)
+{
+	return 0;
+}
+
+static int __hid_bpf_rdesc_fixup(struct hid_bpf_ctx *ctx)
+{
+	return 0;
+}
+
+static struct hid_bpf_ops __bpf_hid_bpf_ops = {
+	.hid_device_event = __hid_bpf_device_event,
+	.hid_rdesc_fixup = __hid_bpf_rdesc_fixup,
+};
+
+static struct bpf_struct_ops bpf_hid_bpf_ops = {
+	.verifier_ops = &hid_bpf_verifier_ops,
+	.init = hid_bpf_ops_init,
+	.check_member = hid_bpf_ops_check_member,
+	.init_member = hid_bpf_ops_init_member,
+	.reg = hid_bpf_reg,
+	.unreg = hid_bpf_unreg,
+	.name = "hid_bpf_ops",
+	.cfi_stubs = &__bpf_hid_bpf_ops,
+	.owner = THIS_MODULE,
+};
+
+void __hid_bpf_ops_destroy_device(struct hid_device *hdev)
+{
+	struct hid_bpf_ops *e;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(e, &hdev->bpf.prog_list, list) {
+		hid_put_device(hdev);
+		e->hdev = NULL;
+	}
+	rcu_read_unlock();
+}
+
+static int __init hid_bpf_struct_ops_init(void)
+{
+	return register_bpf_struct_ops(&bpf_hid_bpf_ops, hid_bpf_ops);
+}
+late_initcall(hid_bpf_struct_ops_init);