Re: [PATCH 02/10] bpf: Add multi kprobe link

[Andrii Nakryiko]

On Tue, Feb 22, 2022 at 9:06 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding new link type BPF_LINK_TYPE_KPROBE_MULTI that attaches kprobe
> program through fprobe API.
>
> The fprobe API allows to attach probe on multiple functions at once
> very fast, because it works on top of ftrace. On the other hand this
> limits the probe point to the function entry or return.
>
> The kprobe program gets the same pt_regs input ctx as when it's attached
> through the perf API.
>
> Adding new attach type BPF_TRACE_KPROBE_MULTI that allows attachment
> kprobe to multiple function with new link.
>
> User provides array of addresses or symbols with count to attach the
> kprobe program to. The new link_create uapi interface looks like:
>
>   struct {
>           __aligned_u64   syms;
>           __aligned_u64   addrs;
>           __u32           cnt;
>           __u32           flags;
>   } kprobe_multi;
>
> The flags field allows single BPF_TRACE_KPROBE_MULTI bit to create
> return multi kprobe.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>

>  include/linux/bpf_types.h      |   1 +
>  include/linux/trace_events.h   |   6 +
>  include/uapi/linux/bpf.h       |  13 ++
>  kernel/bpf/syscall.c           |  26 +++-
>  kernel/trace/bpf_trace.c       | 211 +++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  13 ++
>  6 files changed, 265 insertions(+), 5 deletions(-)
>

[...]

> +
> +static int
> +kprobe_multi_resolve_syms(const void *usyms, u32 cnt,
> +                         unsigned long *addrs)
> +{
> +       unsigned long addr, size;
> +       const char **syms;
> +       int err = -ENOMEM;
> +       unsigned int i;
> +       char *func;
> +
> +       size = cnt * sizeof(*syms);
> +       syms = kvzalloc(size, GFP_KERNEL);
> +       if (!syms)
> +               return -ENOMEM;
> +
> +       func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
> +       if (!func)
> +               goto error;
> +
> +       if (copy_from_user(syms, usyms, size)) {
> +               err = -EFAULT;
> +               goto error;
> +       }
> +
> +       for (i = 0; i < cnt; i++) {
> +               err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
> +               if (err == KSYM_NAME_LEN)
> +                       err = -E2BIG;
> +               if (err < 0)
> +                       goto error;
> +
> +               err = -EINVAL;
> +               if (func[0] == '\0')
> +                       goto error;

wouldn't empty string be handled by kallsyms_lookup_name?

> +               addr = kallsyms_lookup_name(func);
> +               if (!addr)
> +                       goto error;
> +               if (!kallsyms_lookup_size_offset(addr, &size, NULL))
> +                       size = MCOUNT_INSN_SIZE;
> +               addr = ftrace_location_range(addr, addr + size - 1);
> +               if (!addr)
> +                       goto error;
> +               addrs[i] = addr;
> +       }
> +
> +       err = 0;
> +error:
> +       kvfree(syms);
> +       kfree(func);
> +       return err;
> +}
> +

[...]