// 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;
/* prevent multiple attach of the same struct_ops */
if (ops->hdev)
return -EINVAL;
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);
ops->hdev = NULL;
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 int __hid_bpf_hw_request(struct hid_bpf_ctx *ctx, unsigned char reportnum,
enum hid_report_type rtype, enum hid_class_request reqtype,
u64 source)
{
return 0;
}
static int __hid_bpf_hw_output_report(struct hid_bpf_ctx *ctx, u64 source)
{
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,
.hid_hw_request = __hid_bpf_hw_request,
.hid_hw_output_report = __hid_bpf_hw_output_report,
};
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);
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