On 06/02, Yafang Shao wrote:
> By adding support for ->fill_link_info to the kprobe_multi link, users will
> be able to inspect it using `bpftool link show`. This enhancement will
> expose both the count of probed functions and their respective addresses to
> the user.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 4 ++++
> kernel/trace/bpf_trace.c | 26 ++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 4 ++++
> 3 files changed, 34 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a7b5e91..22c8168 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -6438,6 +6438,10 @@ struct bpf_link_info {
> __s32 priority;
> __u32 flags;
> } netfilter;
> + struct {
> + __u64 addrs;
> + __u32 count;
> + } kprobe_multi;
> };
> } __attribute__((aligned(8)));
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 2bc41e6..ec53bc9 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2548,9 +2548,35 @@ 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 *uaddrs = (u64 *)u64_to_user_ptr(info->kprobe_multi.addrs);
Maybe tag this as __user as well?
u64 __user *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
copy_to_user expects __user tagged memory, so most likely sparse tool
will complain on your current approach.
> + 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)
> + return 0;
> + if (ucount != kmulti_link->cnt)
> + return -EINVAL;
[..]
> + if (copy_to_user(uaddrs, kmulti_link->addrs, ucount * sizeof(u64)))
> + return -EFAULT;
I'm not super familiar with this part, so maybe stupid question:
do we need to hold any locks during the copy? IOW, can kmulti_link->addrs
be updated concurrently?
