[RFC,bpf-next,v4,5/7] HID: initial BPF new way implementation

Declare an entry point that can use fmod_ret BPF programs, and
also an API to access and change the incoming data.

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

---

new-ish in v4:
- far from complete, but gives an overview of what we can do now.
---
 drivers/hid/hid-core.c  | 115 ++++++++++++++++++++++++++++++++++++++++
 include/linux/hid_bpf.h |  29 ++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 include/linux/hid_bpf.h

On Thu, Apr 21, 2022 at 04:07:38PM +0200, Benjamin Tissoires wrote:
> Declare an entry point that can use fmod_ret BPF programs, and
> also an API to access and change the incoming data.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> 
> ---
> 
> new-ish in v4:
> - far from complete, but gives an overview of what we can do now.
> ---
>  drivers/hid/hid-core.c  | 115 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/hid_bpf.h |  29 ++++++++++
>  2 files changed, 144 insertions(+)
>  create mode 100644 include/linux/hid_bpf.h
> 
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index db925794fbe6..ff4e1b47d2fb 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -32,6 +32,9 @@
>  #include <linux/hiddev.h>
>  #include <linux/hid-debug.h>
>  #include <linux/hidraw.h>
> +#include <linux/btf.h>
> +#include <linux/btf_ids.h>
> +#include <linux/hid_bpf.h>
>  
>  #include "hid-ids.h"
>  
> @@ -2008,6 +2011,99 @@ int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
>  }
>  EXPORT_SYMBOL_GPL(hid_report_raw_event);
>  
> +struct hid_bpf_ctx_kern {
> +	struct hid_device *hdev;
> +	struct hid_bpf_ctx ctx;
> +	u8 *data;
> +	size_t size;
> +};
> +
> +__weak int hid_bpf_device_event(struct hid_bpf_ctx *ctx, s64 type)
> +{
> +	return 0;
> +}
> +ALLOW_ERROR_INJECTION(hid_bpf_device_event, NS_ERRNO);
> +
> +noinline __u8 *
> +hid_bpf_kfunc_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t __sz)
> +{
> +	struct hid_bpf_ctx_kern *ctx_kern;
> +
> +	if (!ctx)
> +		return NULL;
> +
> +	ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx);
> +
> +	return ctx_kern->data;
> +}

It probably needs to check that "rdonly_buf_sz" or "__sz" constant passed
by the program is less than what was allocated in hid_bpf_ctx_kern->data.
Right?

> +
> +noinline void
> +hid_bpf_kfunc_data_release(__u8 *data)
> +{
> +}

Not clear what release() is for.
hid_bpf_kfunc_get_data() will return PTR_TO_MEM.
There is no need to release it.

> +
> +noinline int
> +hid_bpf_kfunc_hw_request(struct hid_bpf_ctx *ctx)
> +{
> +	if (!ctx)
> +		return -EINVAL;
> +
> +	pr_err("%s test ctx->bus: %04x %s:%d", __func__, ctx->bus, __FILE__, __LINE__);
> +
> +	return 0;
> +}
> +
> +/*
> + * The following set contains all functions we agree BPF programs
> + * can use.
> + */
> +BTF_SET_START(hid_bpf_kfunc_ids)
> +BTF_ID(func, hid_bpf_kfunc_get_data)
> +BTF_ID(func, hid_bpf_kfunc_data_release)
> +BTF_ID(func, hid_bpf_kfunc_hw_request)
> +BTF_SET_END(hid_bpf_kfunc_ids)
> +
> +/*
> + * The following set contains all functions to provide a kernel
> + * resource to the BPF program.
> + * We need to add a counterpart release function.
> + */
> +BTF_SET_START(hid_bpf_kfunc_acquire_ids)
> +BTF_ID(func, hid_bpf_kfunc_get_data)
> +BTF_SET_END(hid_bpf_kfunc_acquire_ids)
> +
> +/*
> + * The following set is the release counterpart of the previous
> + * function set.
> + */
> +BTF_SET_START(hid_bpf_kfunc_release_ids)
> +BTF_ID(func, hid_bpf_kfunc_data_release)
> +BTF_SET_END(hid_bpf_kfunc_release_ids)
> +
> +/*
> + * The following set tells which functions are sleepable.
> + */
> +BTF_SET_START(hid_bpf_kfunc_sleepable_ids)
> +BTF_ID(func, hid_bpf_kfunc_hw_request)
> +BTF_SET_END(hid_bpf_kfunc_sleepable_ids)
> +
> +static const struct btf_kfunc_id_set hid_bpf_kfunc_set = {
> +	.owner         = THIS_MODULE,
> +	.check_set     = &hid_bpf_kfunc_ids,
> +	.acquire_set   = &hid_bpf_kfunc_acquire_ids,
> +	.release_set   = &hid_bpf_kfunc_release_ids,
> +	.ret_null_set  = &hid_bpf_kfunc_acquire_ids, /* duplicated to force BPF programs to
> +						      * check the validity of the returned pointer
> +						      * in acquire function
> +						      */
> +	.sleepable_set = &hid_bpf_kfunc_sleepable_ids,
> +};
> +
> +static int __init hid_bpf_init(void)
> +{
> +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &hid_bpf_kfunc_set);
> +}
> +
>  /**
>   * hid_input_report - report data from lower layer (usb, bt...)
>   *
> @@ -2025,6 +2121,17 @@ int hid_input_report(struct hid_device *hid, int type, u8 *data, u32 size, int i
>  	struct hid_driver *hdrv;
>  	struct hid_report *report;
>  	int ret = 0;
> +	struct hid_bpf_ctx_kern ctx_kern = {
> +		.hdev = hid,
> +		.ctx = {
> +			.bus = hid->bus,
> +			.group = hid->group,
> +			.vendor = hid->vendor,
> +			.product = hid->product,
> +		},
> +		.data = data,
> +		.size = size,
> +	};

I'm not sure why hid_bpf_ctx_kern is needed.
Just to scope all args into one struct?

> +/*
> + * The following is the HID BPF API.
> + *
> + * It should be treated as UAPI, so extra care is required
> + * when making change to this file.
> + */
> +
> +struct hid_bpf_ctx {
> +	__u16 bus;							/* BUS ID */
> +	__u16 group;							/* Report group */
> +	__u32 vendor;							/* Vendor ID */
> +	__u32 product;							/* Product ID */
> +	__u32 version;							/* HID version */
> +};

Your choice of course,
but not clear why kernel has to populate it with explicit:
+			.bus = hid->bus,
+			.group = hid->group,
+			.vendor = hid->vendor,
+			.product = hid->product,
and waste cpu cycles on that while bpf program can read all these fields
on demand when necessary.