Re: [PATCH] xen/kexec: return error code for unknown hypercalls

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/02/2026 6:31 pm, Roger Pau Monne wrote:
> Currently do_kexec_op_internal() will return 0 for unknown hypercalls.  Fix
> this by returning -EOPNOTSUPP instead.
>
> Fixes: d046f361dc93 ("Xen Security Modules: XSM")
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

> ---
> Arguably the error code for unsupported kexec hypercalls was already wonky
> before the XSM addiiton, as it would return -EINVAL.  It's however way
> worse after the XSM addition, as it returns 0.
> ---
>  xen/common/kexec.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/xen/common/kexec.c b/xen/common/kexec.c
> index 84fe8c35976e..8f52c5506d4a 100644
> --- a/xen/common/kexec.c
> +++ b/xen/common/kexec.c
> @@ -1217,9 +1217,8 @@ static int do_kexec_op_internal(unsigned long op,
>                                  XEN_GUEST_HANDLE_PARAM(void) uarg,
>                                  bool compat)
>  {
> -    int ret = -EINVAL;
> +    int ret = xsm_kexec(XSM_PRIV);
>  
> -    ret = xsm_kexec(XSM_PRIV);
>      if ( ret )
>          return ret;

Personally, I'd just have `int ret;` and leave the xsm_kexec() call as
it was.  That leaves the slightly more normal pattern intact.

>  
> @@ -1258,6 +1257,10 @@ static int do_kexec_op_internal(unsigned long op,
>      case KEXEC_CMD_kexec_status:
>          ret = kexec_status(uarg);
>          break;
> +
> +    default:
> +        ret = -EOPNOTSUPP;
> +        break;
>      }
>  
>      clear_bit(KEXEC_FLAG_IN_HYPERCALL, &kexec_flags);