Re: [PATCH bpf-next v7 13/24] HID: initial BPF implementation

Benjamin Tissoires
2022-08-24T09:49:01Z

On 7/28/22 16:19, Greg KH wrote:
> On Thu, Jul 21, 2022 at 05:36:14PM +0200, Benjamin Tissoires wrote:
>> --- /dev/null
>> +++ b/include/linux/hid_bpf.h
>> @@ -0,0 +1,102 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
>
> This is not a uapi .h file, so the "WITH Linux-syscall-note" should not
> be here, right?

thanks, dropping this syscall note from the series.

>
>
>> +
>> +#ifndef __HID_BPF_H
>> +#define __HID_BPF_H
>> +
>> +#include <linux/spinlock.h>
>> +#include <uapi/linux/hid.h>
>> +#include <uapi/linux/hid_bpf.h>
>> +
>> +struct hid_device;
>> +
>> +/*
>> + * The following is the HID BPF API.
>> + *
>> + * It should be treated as UAPI, so extra care is required
>> + * when making change to this file.
>
> So is this uapi? If so, shouldn't it go into a uapi include directory
> so we know this and properly track it and maintain it that way?

IMO it's a grey area. It is not "uapi" because it doesn't export
anything that userspace can use. A userspace program can not include
that and use it in other words.

So strictly speaking, it's a normal part of a kernel header file,
because it's a description of what other kernel users (though here, eBPF
programs) can use.

But I really want that part of the API to be considered as "stable" and
give some guarantees to the users that I won't change it at every
release. Thus the "uapi-like".

>
>> + */
>> +
>> +/**
>> + * struct hid_bpf_ctx - User accessible data for all HID programs
>> + *
>> + * ``data`` is not directly accessible from the context. We need to issue
>> + * a call to ``hid_bpf_get_data()`` in order to get a pointer to that field.
>> + *
>> + * All of these fields are currently read-only.
>> + *
>> + * @index: program index in the jump table. No special meaning (a smaller index
>> + * doesn't mean the program will be executed before another program with
>> + * a bigger index).
>> + * @hid: the ``struct hid_device`` representing the device itself
>> + * @report_type: used for ``hid_bpf_device_event()``
>> + * @size: Valid data in the data field.
>> + *
>> + * Programs can get the available valid size in data by fetching this field.
>> + */
>> +struct hid_bpf_ctx {
>> + __u32 index;
>> + const struct hid_device *hid;
>> + enum hid_report_type report_type;
>> + __s32 size;
>> +};
>> +
>> +/* Following functions are tracepoints that BPF programs can attach to */
>> +int hid_bpf_device_event(struct hid_bpf_ctx *ctx);
>> +
>> +/* Following functions are kfunc that we export to BPF programs */
>> +/* only available in tracing */
>> +__u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t __sz);
>> +
>> +/* only available in syscall */
>> +int hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags);
>> +
>> +/*
>> + * Below is HID internal
>> + */
>> +
>> +/* internal function to call eBPF programs, not to be used by anybody */
>> +int __hid_bpf_tail_call(struct hid_bpf_ctx *ctx);
>> +
>> +#define HID_BPF_MAX_PROGS_PER_DEV 64
>> +#define HID_BPF_FLAG_MASK (((HID_BPF_FLAG_MAX - 1) << 1) - 1)
>> +
>> +/* types of HID programs to attach to */
>> +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_MAX,
>> +};
>> +
>> +struct hid_bpf_ops {
>> + struct module *owner;
>> + struct bus_type *bus_type;
>> +};
>> +
>> +extern struct hid_bpf_ops *hid_bpf_ops;
>> +
>> +struct hid_bpf_prog_list {
>> + u16 prog_idx[HID_BPF_MAX_PROGS_PER_DEV];
>> + u8 prog_cnt;
>> +};
>> +
>> +/* stored in each device */
>> +struct hid_bpf {
>> + struct hid_bpf_prog_list __rcu *progs[HID_BPF_PROG_TYPE_MAX]; /* attached BPF progs */
>> + bool destroyed; /* prevents the assignment of any progs */
>> +
>> + spinlock_t progs_lock; /* protects RCU update of progs */
>> +};
>> +
>> +#ifdef CONFIG_HID_BPF
>> +int dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
>> + u32 size, int interrupt);
>> +void hid_bpf_destroy_device(struct hid_device *hid);
>> +void hid_bpf_device_init(struct hid_device *hid);
>> +#else /* CONFIG_HID_BPF */
>> +static inline int dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
>> + u32 size, int interrupt) { return 0; }
>> +static inline void hid_bpf_destroy_device(struct hid_device *hid) {}
>> +static inline void hid_bpf_device_init(struct hid_device *hid) {}
>> +#endif /* CONFIG_HID_BPF */
>> +
>> +#endif /* __HID_BPF_H */
>> diff --git a/include/uapi/linux/hid_bpf.h b/include/uapi/linux/hid_bpf.h
>> new file mode 100644
>> index 000000000000..ba8caf9b60ee
>> --- /dev/null
>> +++ b/include/uapi/linux/hid_bpf.h
>> @@ -0,0 +1,25 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>
> This is fine, it is in include/uapi/
>
> Other than those minor comments, this all looks good to me!
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>

Great!
And thanks a lot for the other reviews.

I finally managed to get some time to work on it after some time off and
urgent sh**t happening, so I'll send a new version of the series today.

Cheers,
Benjamin