[PATCH] x86/hvm: Fix use-after-free introduced by c/s 428607a

[Andrew Cooper <andrew.cooper3@citrix.com>]

c/s 428607a "x86: shrink 'struct domain', was already PAGE_SIZE" introduced a
use-after-free error during domain destruction, because of the order in which
timers are torn down.

  (XEN) Xen call trace:
  (XEN)    [<ffff82d08013344e>] spinlock.c#check_lock+0x1e/0x40
  (XEN)    [<ffff82d08013349b>] _spin_lock+0x11/0x52
  (XEN)    [<ffff82d0801e8076>] vpt.c#pt_lock+0x24/0x40
  (XEN)    [<ffff82d0801e88f4>] destroy_periodic_time+0x18/0x81
  (XEN)    [<ffff82d0801e1089>] rtc_deinit+0x53/0x78
  (XEN)    [<ffff82d0801d1e5a>] hvm_domain_destroy+0x52/0x69
  (XEN)    [<ffff82d08016a758>] arch_domain_destroy+0x1a/0x98
  (XEN)    [<ffff82d080107cd5>] domain.c#complete_domain_destroy+0x6f/0x182
  (XEN)    [<ffff82d080126a19>] rcupdate.c#rcu_process_callbacks+0x144/0x1a6
  (XEN)    [<ffff82d080132c52>] softirq.c#__do_softirq+0x82/0x8d
  (XEN)    [<ffff82d080132caa>] do_softirq+0x13/0x15
  (XEN)    [<ffff82d080248ae1>] entry.o#process_softirqs+0x21/0x30
  (XEN)
  (XEN)
  (XEN) ****************************************
  (XEN) Panic on CPU 3:
  (XEN) GENERAL PROTECTION FAULT
  (XEN) [error_code=0000]
  (XEN) ****************************************

Defer the freeing of d->arch.hvm_domain.pl_time until all timers have been
destroyed.

For safety, NULL out the pointers after freeing them, in an attempt to make
mistakes more obvious in the future.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Corneliu ZUZU <czuzu@bitdefender.com>
---
 xen/arch/x86/hvm/hvm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index f24400d..38c65b3 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1674,8 +1674,10 @@ void hvm_domain_relinquish_resources(struct domain *d)
 void hvm_domain_destroy(struct domain *d)
 {
     xfree(d->arch.hvm_domain.io_handler);
+    d->arch.hvm_domain.io_handler = NULL;
+
     xfree(d->arch.hvm_domain.params);
-    xfree(d->arch.hvm_domain.pl_time);
+    d->arch.hvm_domain.params = NULL;
 
     hvm_destroy_cacheattr_region_list(d);
 
@@ -1686,6 +1688,9 @@ void hvm_domain_destroy(struct domain *d)
     rtc_deinit(d);
     stdvga_deinit(d);
     vioapic_deinit(d);
+
+    xfree(d->arch.hvm_domain.pl_time);
+    d->arch.hvm_domain.pl_time = NULL;
 }
 
 static int hvm_save_tsc_adjust(struct domain *d, hvm_domain_context_t *h)
-- 
2.1.4