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

[Benjamin Tissoires]

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@xxxxxxxxxxxxxxxxxxx>

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