Re: [PATCH v3 bpf-next 01/10] bpf: Support ->fill_link_info for kprobe_multi

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Jun 12, 2023 at 03:15:59PM +0000, Yafang Shao wrote:

SNIP

> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 2bc41e6..742047c 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2548,9 +2548,36 @@ static void bpf_kprobe_multi_link_dealloc(struct bpf_link *link)
>  	kfree(kmulti_link);
>  }
>  
> +static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
> +						struct bpf_link_info *info)
> +{
> +	u64 __user *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
> +	struct bpf_kprobe_multi_link *kmulti_link;
> +	u32 ucount = info->kprobe_multi.count;
> +
> +	if (!uaddrs ^ !ucount)
> +		return -EINVAL;
> +
> +	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
> +	if (!uaddrs) {
> +		info->kprobe_multi.count = kmulti_link->cnt;
> +		return 0;
> +	}
> +
> +	if (ucount < kmulti_link->cnt)
> +		return -EINVAL;
> +	info->kprobe_multi.flags = kmulti_link->fp.flags;
> +	if (!kallsyms_show_value(current_cred()))
> +		return 0;
> +	if (copy_to_user(uaddrs, kmulti_link->addrs, ucount * sizeof(u64)))
> +		return -EFAULT;
> +	return 0;
> +}
> +
>  static const struct bpf_link_ops bpf_kprobe_multi_link_lops = {
>  	.release = bpf_kprobe_multi_link_release,
>  	.dealloc = bpf_kprobe_multi_link_dealloc,
> +	.fill_link_info = bpf_kprobe_multi_link_fill_link_info,
>  };
>  
>  static void bpf_kprobe_multi_cookie_swap(void *a, void *b, int size, const void *priv)
> @@ -2890,6 +2917,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  		return err;
>  	}
>  
> +	link->fp.flags = flags;

hum this looks wrong, we can't use fprobe flags to store our flags
you should add flags to bpf_kprobe_multi_link

jirka

>  	return bpf_link_settle(&link_primer);
>  
>  error:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index a7b5e91..23691ea 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -6438,6 +6438,11 @@ struct bpf_link_info {
>  			__s32 priority;
>  			__u32 flags;
>  		} netfilter;
> +		struct {
> +			__aligned_u64 addrs; /* in/out: addresses buffer ptr */
> +			__u32 count;
> +			__u32 flags;
> +		} kprobe_multi;
>  	};
>  } __attribute__((aligned(8)));
>  
> -- 
> 1.8.3.1
>