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

Yonghong Song
2022-05-17T07:09:59Z

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;
> }