data->data can be NULL when len is 0. Strictly speaking, the behavior
of memcpy() in such a scenario is undefined so UBSan complaints.

Satisfy UBSan by checking if len is 0 before memcpy().

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 hw/i386/kvm/xen_xenstore.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index 59691056670e..17802aa33d20 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -532,6 +532,10 @@ static void xs_read(XenXenstoreState *s, unsigned int req_id,
         return;
     }
 
+    if (!len) {
+        return;
+    }
+
     memcpy(&rsp_data[rsp->len], data->data, len);
     rsp->len += len;
 }

---
base-commit: 38d0939b86e2eef6f6a622c6f1f7befda0146595
change-id: 20241227-xen-fb5a15cc0ca7

Best regards,
-- 
Akihiko Odaki <akihiko.odaki@daynix.com>

On Wed, 2025-01-08 at 20:31 +0900, Akihiko Odaki wrote:
> data->data can be NULL when len is 0. Strictly speaking, the behavior
> of memcpy() in such a scenario is undefined so UBSan complaints.
> 
> Satisfy UBSan by checking if len is 0 before memcpy().
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>

Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>

Thanks.

> ---
>  hw/i386/kvm/xen_xenstore.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
> index 59691056670e..17802aa33d20 100644
> --- a/hw/i386/kvm/xen_xenstore.c
> +++ b/hw/i386/kvm/xen_xenstore.c
> @@ -532,6 +532,10 @@ static void xs_read(XenXenstoreState *s,
> unsigned int req_id,
>          return;
>      }
>  
> +    if (!len) {
> +        return;
> +    }
> +
>      memcpy(&rsp_data[rsp->len], data->data, len);
>      rsp->len += len;
>  }
> 
> ---
> base-commit: 38d0939b86e2eef6f6a622c6f1f7befda0146595
> change-id: 20241227-xen-fb5a15cc0ca7
> 
> Best regards,

On 8/1/25 12:31, Akihiko Odaki wrote:
> data->data can be NULL when len is 0. Strictly speaking, the behavior
> of memcpy() in such a scenario is undefined so UBSan complaints.
> 
> Satisfy UBSan by checking if len is 0 before memcpy().
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>   hw/i386/kvm/xen_xenstore.c | 4 ++++
>   1 file changed, 4 insertions(+)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>