linux-kernel - Re: [PATCH bpf-next v3 2/4] bpf_trace: support 32-bit kernels in bpf_kprobe_multi_link

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Message-ID: <CAEf4BzZVe2k1q-XrTwq=OMvcFRdZSfYa0bv1occxR0NX_Ax2rA@mail.gmail.com>
Date:   Wed, 18 May 2022 16:31:13 -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 2/4] bpf_trace: support 32-bit kernels in bpf_kprobe_multi_link_attach

On Tue, May 17, 2022 at 12:36 AM Eugene Syromiatnikov <esyr@...hat.com> wrote:
>
> It seems that there is no reason not to support 32-bit architectures;
> doing so requires a bit of rework with respect to cookies handling,
> however, as the current code implicitly assumes
> that sizeof(long) == sizeof(u64).
>
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
>  kernel/trace/bpf_trace.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 9c041be..a93a54f 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2435,16 +2435,12 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>         struct bpf_link_primer link_primer;
>         void __user *ucookies;
>         unsigned long *addrs;
> -       u32 flags, cnt, size;
> +       u32 flags, cnt, size, cookies_size;
>         void __user *uaddrs;
>         u64 *cookies = NULL;
>         void __user *usyms;
>         int err;
>
> -       /* no support for 32bit archs yet */
> -       if (sizeof(u64) != sizeof(void *))
> -               return -EOPNOTSUPP;
> -
>         if (prog->expected_attach_type != BPF_TRACE_KPROBE_MULTI)
>                 return -EINVAL;
>
> @@ -2454,6 +2450,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>
>         uaddrs = u64_to_user_ptr(attr->link_create.kprobe_multi.addrs);
>         usyms = u64_to_user_ptr(attr->link_create.kprobe_multi.syms);
> +       ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
>         if (!!uaddrs == !!usyms)
>                 return -EINVAL;
>
> @@ -2461,8 +2458,11 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>         if (!cnt)
>                 return -EINVAL;
>
> -       if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> +       if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size) ||
> +           (ucookies &&
> +            check_mul_overflow(cnt, (u32)sizeof(*cookies), &cookies_size))) {
>                 return -EOVERFLOW;
> +       }
>         addrs = kvmalloc(size, GFP_KERNEL);
>         if (!addrs)
>                 return -ENOMEM;
> @@ -2486,14 +2486,13 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>                         goto error;
>         }
>
> -       ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
>         if (ucookies) {
> -               cookies = kvmalloc(size, GFP_KERNEL);
> +               cookies = kvmalloc(cookies_size, GFP_KERNEL);

same question about consistent use of kvmalloc_array() and delegating
all the overflow checks to it?

>                 if (!cookies) {
>                         err = -ENOMEM;
>                         goto error;
>                 }
> -               if (copy_from_user(cookies, ucookies, size)) {
> +               if (copy_from_user(cookies, ucookies, cookies_size)) {
>                         err = -EFAULT;
>                         goto error;
>                 }
> --
> 2.1.4
>