Re: [PATCH bpf v2 2/4] bpf_trace: support 32-bit kernels in bpf_kprobe_multi_link_attach

[Yonghong Song <yhs@fb.com>]

On 5/16/22 4:05 PM, 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@redhat.com>
> ---
>   kernel/trace/bpf_trace.c | 18 +++++++++---------
>   1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index f1d4e68..bf5bcfb 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2406,16 +2406,12 @@ 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;
>   
> @@ -2425,6 +2421,7 @@ 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;
>   
> @@ -2432,8 +2429,11 @@ 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;
> +	}
>   	size = cnt * sizeof(*addrs);

size has been calculated, no need to calculate again.

>   	addrs = kvmalloc(size, GFP_KERNEL);
>   	if (!addrs)
> @@ -2450,14 +2450,14 @@ 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_size = cnt * sizeof(*cookies);

same for cookies_size.

> +		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;
>   		}