[xen staging] xen: fix XEN_DOMCTL_gdbsx_guestmemio crash

[patchbot@xxxxxxx]

commit f00daf1fb3213a9b0335d9dcd90fe9cb5c02b7a9
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Apr 19 15:52:52 2022 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Apr 19 17:07:08 2022 +0100

    xen: fix XEN_DOMCTL_gdbsx_guestmemio crash
    
    A hypervisor built without CONFIG_GDBSX will crash in case the
    XEN_DOMCTL_gdbsx_guestmemio domctl is being called, as the call will
    end up in iommu_do_domctl() with d == NULL:
    
      (XEN) CPU:    6
      (XEN) RIP:    e008:[<ffff82d040269984>] iommu_do_domctl+0x4/0x30
      (XEN) RFLAGS: 0000000000010202   CONTEXT: hypervisor (d0v0)
      (XEN) rax: 00000000000003e8   rbx: ffff830856277ef8   rcx: 
ffff830856277fff
      ...
      (XEN) Xen call trace:
      (XEN)    [<ffff82d040269984>] R iommu_do_domctl+0x4/0x30
      (XEN)    [<ffff82d04035cd5f>] S arch_do_domctl+0x7f/0x2330
      (XEN)    [<ffff82d040239e46>] S do_domctl+0xe56/0x1930
      (XEN)    [<ffff82d040238ff0>] S do_domctl+0/0x1930
      (XEN)    [<ffff82d0402f8c59>] S pv_hypercall+0x99/0x110
      (XEN)    [<ffff82d0402f5161>] S 
arch/x86/pv/domain.c#_toggle_guest_pt+0x11/0x90
      (XEN)    [<ffff82d040366288>] S lstar_enter+0x128/0x130
      (XEN)
      (XEN) Pagetable walk from 0000000000000144:
      (XEN)  L4[0x000] = 0000000000000000 ffffffffffffffff
      (XEN)
      (XEN) ****************************************
      (XEN) Panic on CPU 6:
      (XEN) FATAL PAGE FAULT
      (XEN) [error_code=0000]
      (XEN) Faulting linear address: 0000000000000144
      (XEN) ****************************************
    
    It used to be permitted to pass DOMID_IDLE to dbg_rw_mem(), which is why the
    special case skipping the domid checks exists.  Now that it is only 
permitted
    to pass proper domids, remove the special case, making 'd' always valid.
    
    Reported-by: Cheyenne Wills <cheyenne.wills@xxxxxxxxx>
    Fixes: e726a82ca0dc ("xen: make gdbsx support configurable")
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/common/domctl.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 57135d4478..5879117580 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -308,7 +308,6 @@ long cf_check 
do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         if ( op->domain == DOMID_INVALID )
         {
     case XEN_DOMCTL_createdomain:
-    case XEN_DOMCTL_gdbsx_guestmemio:
             d = NULL;
             break;
         }
--
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