x86/HAP: adjust monitor table related error handling

hap_make_monitor_table() will return INVALID_MFN if it encounters an
error condition, but hap_update_paging_modes() wasn’t handling this
value, resulting in an inappropriate value being stored in
monitor_table. This would subsequently misguide at least
hap_vcpu_teardown(). Avoid this by bailing early.

Further, when a domain has/was already crashed or (perhaps less
important as there's no such path known to lead here) is already dying,
avoid calling domain_crash() on it again - that's at best confusing.

This is part of CVE-2022-33746 / XSA-410.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 5b44a61180
master date: 2022-10-11 14:21:56 +0200

xen/arch/x86/mm/hap/hap.c

@@ -39,6 +39,7 @@
 #include <asm/domain.h>
 #include <xen/numa.h>
 #include <asm/hvm/nestedhvm.h>
+#include <public/sched.h>
 
 #include "private.h"
 
@@ -405,8 +406,13 @@ static mfn_t hap_make_monitor_table(struct vcpu *v)
     return m4mfn;
 
  oom:
-    printk(XENLOG_G_ERR "out of memory building monitor pagetable\n");
-    domain_crash(d);
+    if ( !d->is_dying &&
+         (!d->is_shutting_down || d->shutdown_code != SHUTDOWN_crash) )
+    {
+        printk(XENLOG_G_ERR "%pd: out of memory building monitor pagetable\n",
+               d);
+        domain_crash(d);
+    }
     return INVALID_MFN;
 }
 
@@ -766,6 +772,9 @@ static void hap_update_paging_modes(struct vcpu *v)
     if ( pagetable_is_null(v->arch.hvm.monitor_table) )
     {
         mfn_t mmfn = hap_make_monitor_table(v);
+
+        if ( mfn_eq(mmfn, INVALID_MFN) )
+            goto unlock;
         v->arch.hvm.monitor_table = pagetable_from_mfn(mmfn);
         make_cr3(v, mmfn);
         hvm_update_host_cr3(v);
@@ -774,6 +783,7 @@ static void hap_update_paging_modes(struct vcpu *v)
     /* CR3 is effectively updated by a mode change. Flush ASIDs, etc. */
     hap_update_cr3(v, 0, false);
 
+ unlock:
     paging_unlock(d);
     put_gfn(d, cr3_gfn);
 }