Re: [RFC PATCH bpf-next 2/8] bpf: Support ->fill_link_info for kprobe_multi

From: Jiri Olsa <olsajiri@gmail.com>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
	andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
	yhs@fb.com, kpsingh@kernel.org, sdf@google.com,
	haoluo@google.com, quentin@isovalent.com, bpf@vger.kernel.org
Subject: Re: [RFC PATCH bpf-next 2/8] bpf: Support ->fill_link_info for kprobe_multi
Date: Mon, 29 May 2023 14:49:53 +0200	[thread overview]
Message-ID: <ZHSfcabMuoy17ill@krava> (raw)
In-Reply-To: <20230528142027.5585-3-laoar.shao@gmail.com>

On Sun, May 28, 2023 at 02:20:21PM +0000, Yafang Shao wrote:

SNIP

> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0d84a7a..00a0009 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2564,10 +2564,41 @@ static void bpf_kprobe_multi_link_show_fdinfo(const struct bpf_link *link,
>  	}
>  }
>  
> +static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
> +						struct bpf_link_info *info)
> +{
> +	struct bpf_kprobe_multi_link *kmulti_link;
> +	u64 *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
> +	u32 ucount = info->kprobe_multi.count;
> +	int i;
> +
> +	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)
> +		return 0;
> +
> +	if (ucount != kmulti_link->cnt)
> +		return -EINVAL;
> +
> +	for (i = 0; i < ucount; i++)
> +		if (copy_to_user(uaddrs + i, kmulti_link->addrs + i,
> +				 sizeof(u64)))
> +			return -EFAULT;

let's use put_user instead copy_to_user? or even better why not
copy that with single copy_to_user from kmulti_link->addrs

jirka

> +	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,
>  	.show_fdinfo = bpf_kprobe_multi_link_show_fdinfo,
> +	.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)
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 9273c65..6be9b1d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -6434,6 +6434,10 @@ struct bpf_link_info {
>  			__s32 priority;
>  			__u32 flags;
>  		} netfilter;
> +		struct {
> +			__aligned_u64 addrs;
> +			__u32 count;
> +		} kprobe_multi;
>  	};
>  } __attribute__((aligned(8)));
>  
> -- 
> 1.8.3.1
> 