linux-kernel - Re: [PATCH bpf-next v3 3/4] bpf_trace: handle compat in copy_user

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Message-ID: <CAEf4BzbnWM9BfQwjQtgwjx+OXBEkejxs2czz3DQbeoCAXPj11g@mail.gmail.com>
Date:   Wed, 18 May 2022 16:39:58 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 3/4] bpf_trace: handle compat in copy_user_syms

On Tue, May 17, 2022 at 12:36 AM Eugene Syromiatnikov <esyr@...hat.com> wrote:
>
> For compat processes, userspace size for syms pointers is different.
> Provide compat handling for copying array elements from the user space.
>
> Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
>  kernel/trace/bpf_trace.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index a93a54f..9d3028a 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2253,6 +2253,24 @@ struct user_syms {
>         char *buf;
>  };
>
> +static inline int get_arr_ptr(unsigned long *p,
> +                             unsigned long __user *uaddr, u32 idx)

no need for inline, let compiler decide on inlining

> +{
> +       if (unlikely(in_compat_syscall())) {

not sure unlikely() is justified for code...

> +               compat_uptr_t __user *compat_uaddr = (compat_uptr_t __user *)uaddr;
> +               compat_uptr_t val;
> +               int err;
> +
> +               err = __get_user(val, compat_uaddr + idx);
> +               if (!err)
> +                       *p = val;
> +
> +               return err;
> +       } else {
> +               return __get_user(*p, uaddr + idx);
> +       }
> +}
> +
>  static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
>  {
>         unsigned long __user usymbol;
> @@ -2270,7 +2288,7 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
>                 goto error;
>
>         for (p = buf, i = 0; i < cnt; i++) {
> -               if (__get_user(usymbol, usyms + i)) {
> +               if (get_arr_ptr(&usymbol, usyms, i)) {
>                         err = -EFAULT;
>                         goto error;
>                 }
> --
> 2.1.4
>