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

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Date:   Tue, 17 May 2022 11:12:47 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     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>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, 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 09:36:26AM +0200, Eugene Syromiatnikov 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) {

could we check all that in here? so the ucookies checks are on the
one place.. also you would not need cookies_size

jirka

> -		cookies = kvmalloc(size, GFP_KERNEL);
> +		cookies = kvmalloc(cookies_size, GFP_KERNEL);
>  		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
>