[PATCH v2 3/7] x86/vm-event/monitor: don't compromise monitor_write_data on domain cleanup

From: Corneliu ZUZU <czuzu@bitdefender.com>
To: xen-devel@lists.xen.org
Cc: Tamas K Lengyel <tamas@tklengyel.com>,
	Razvan Cojocaru <rcojocaru@bitdefender.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Paul Durrant <paul.durrant@citrix.com>,
	Jan Beulich <jbeulich@suse.com>
Subject: [PATCH v2 3/7] x86/vm-event/monitor: don't compromise monitor_write_data on domain cleanup
Date: Tue,  5 Jul 2016 17:28:22 +0300	[thread overview]
Message-ID: <1467728902-13725-1-git-send-email-czuzu@bitdefender.com> (raw)
In-Reply-To: <1467728717-13592-1-git-send-email-czuzu@bitdefender.com>

The arch_vm_event structure is dynamically allocated and freed @
vm_event_cleanup_domain. This cleanup is triggered e.g. when the toolstack user
disables domain monitoring (xc_monitor_disable), which in turn effectively
discards any information that was in arch_vm_event.write_data.

But this can yield unexpected behavior since if a CR-write was awaiting to be
committed on the scheduling tail (hvm_do_resume->arch_monitor_write_data)
before xc_monitor_disable is called, then the domain CR write is wrongfully
ignored, which of course, in these cases, can easily render a domain crash.

To fix the issue, this patch makes arch_vm_event.emul_read_data dynamically
allocated and only frees that in vm_event_cleanup_domain, instead of the whole
arch_vcpu.vm_event structure, which with this patch will only be freed on
vcpu/domain destroyal.

Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
---
Changed since v1:
  * arch_vcpu.vm_event made pointer again to avoid eating memory from arch_vcpu
    structure
---
 xen/arch/x86/domain.c          |  9 +++++++--
 xen/arch/x86/hvm/emulate.c     |  6 +++---
 xen/arch/x86/hvm/hvm.c         |  2 ++
 xen/arch/x86/mm/p2m.c          |  2 +-
 xen/arch/x86/vm_event.c        | 22 ++++++++++++++++------
 xen/common/vm_event.c          | 11 +++++++++++
 xen/include/asm-x86/monitor.h  |  4 +++-
 xen/include/asm-x86/vm_event.h |  2 +-
 8 files changed, 44 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index bb59247..0313208 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -56,6 +56,7 @@
 #include <asm/debugreg.h>
 #include <asm/msr.h>
 #include <asm/traps.h>
+#include <asm/vm_event.h>
 #include <asm/nmi.h>
 #include <asm/mce.h>
 #include <asm/amd.h>
@@ -492,8 +493,12 @@ int vcpu_initialise(struct vcpu *v)
 
 void vcpu_destroy(struct vcpu *v)
 {
-    xfree(v->arch.vm_event);
-    v->arch.vm_event = NULL;
+    if ( unlikely(v->arch.vm_event) )
+    {
+        xfree(v->arch.vm_event->emul_read_data);
+        xfree(v->arch.vm_event);
+        v->arch.vm_event = NULL;
+    }
 
     if ( is_pv_32bit_vcpu(v) )
     {
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 855af4d..3880df1 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -73,12 +73,12 @@ static int set_context_data(void *buffer, unsigned int size)
 {
     struct vcpu *curr = current;
 
-    if ( curr->arch.vm_event )
+    if ( curr->arch.vm_event && curr->arch.vm_event->emul_read_data )
     {
         unsigned int safe_size =
-            min(size, curr->arch.vm_event->emul_read_data.size);
+            min(size, curr->arch.vm_event->emul_read_data->size);
 
-        memcpy(buffer, curr->arch.vm_event->emul_read_data.data, safe_size);
+        memcpy(buffer, curr->arch.vm_event->emul_read_data->data, safe_size);
         memset(buffer + safe_size, 0, size - safe_size);
         return X86EMUL_OKAY;
     }
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index e3829d2..ac6d9eb 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -479,6 +479,8 @@ void hvm_do_resume(struct vcpu *v)
         {
             enum emul_kind kind = EMUL_KIND_NORMAL;
 
+            ASSERT(v->arch.vm_event->emul_read_data);
+
             if ( v->arch.vm_event->emulate_flags &
                  VM_EVENT_FLAG_SET_EMUL_READ_DATA )
                 kind = EMUL_KIND_SET_CONTEXT;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 16733a4..6616626 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1642,7 +1642,7 @@ void p2m_mem_access_emulate_check(struct vcpu *v,
         v->arch.vm_event->emulate_flags = violation ? rsp->flags : 0;
 
         if ( (rsp->flags & VM_EVENT_FLAG_SET_EMUL_READ_DATA) )
-            v->arch.vm_event->emul_read_data = rsp->data.emul_read_data;
+            *v->arch.vm_event->emul_read_data = rsp->data.emul_read_data;
     }
 }
 
diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 80f84d6..0e25e4d 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -30,12 +30,18 @@ int vm_event_init_domain(struct domain *d)
 
     for_each_vcpu ( d, v )
     {
-        if ( v->arch.vm_event )
+        if ( likely(!v->arch.vm_event) )
+        {
+            v->arch.vm_event = xzalloc(struct arch_vm_event);
+            if ( !v->arch.vm_event )
+                return -ENOMEM;
+        }
+        else if ( unlikely(v->arch.vm_event->emul_read_data) )
             continue;
 
-        v->arch.vm_event = xzalloc(struct arch_vm_event);
-
-        if ( !v->arch.vm_event )
+        v->arch.vm_event->emul_read_data =
+                xzalloc(struct vm_event_emul_read_data);
+        if ( !v->arch.vm_event->emul_read_data )
             return -ENOMEM;
     }
 
@@ -52,8 +58,12 @@ void vm_event_cleanup_domain(struct domain *d)
 
     for_each_vcpu ( d, v )
     {
-        xfree(v->arch.vm_event);
-        v->arch.vm_event = NULL;
+        if ( likely(!v->arch.vm_event) )
+            continue;
+
+        v->arch.vm_event->emulate_flags = 0;
+        xfree(v->arch.vm_event->emul_read_data);
+        v->arch.vm_event->emul_read_data = NULL;
     }
 
     d->arch.mem_access_emulate_each_rep = 0;
diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
index 17d2716..75bbbab 100644
--- a/xen/common/vm_event.c
+++ b/xen/common/vm_event.c
@@ -534,6 +534,8 @@ static void mem_sharing_notification(struct vcpu *v, unsigned int port)
 /* Clean up on domain destruction */
 void vm_event_cleanup(struct domain *d)
 {
+    struct vcpu *v;
+
 #ifdef CONFIG_HAS_MEM_PAGING
     if ( d->vm_event->paging.ring_page )
     {
@@ -560,6 +562,15 @@ void vm_event_cleanup(struct domain *d)
         (void)vm_event_disable(d, &d->vm_event->share);
     }
 #endif
+
+    for_each_vcpu ( d, v )
+    {
+        if ( unlikely(v->arch.vm_event) )
+        {
+            xfree(v->arch.vm_event);
+            v->arch.vm_event = NULL;
+        }
+    }
 }
 
 int vm_event_domctl(struct domain *d, xen_domctl_vm_event_op_t *vec,
diff --git a/xen/include/asm-x86/monitor.h b/xen/include/asm-x86/monitor.h
index 0611681..a094c0d 100644
--- a/xen/include/asm-x86/monitor.h
+++ b/xen/include/asm-x86/monitor.h
@@ -26,6 +26,7 @@
 #include <public/domctl.h>
 #include <asm/cpufeature.h>
 #include <asm/hvm/hvm.h>
+#include <asm/vm_event.h>
 
 #define monitor_ctrlreg_bitmask(ctrlreg_index) (1U << (ctrlreg_index))
 
@@ -48,7 +49,8 @@ int arch_monitor_domctl_op(struct domain *d, struct xen_domctl_monitor_op *mop)
          * Enabling mem_access_emulate_each_rep without a vm_event subscriber
          * is meaningless.
          */
-        if ( d->max_vcpus && d->vcpu[0] && d->vcpu[0]->arch.vm_event )
+        if ( d->max_vcpus && d->vcpu[0] && d->vcpu[0]->arch.vm_event &&
+             d->vcpu[0]->arch.vm_event->emul_read_data )
             d->arch.mem_access_emulate_each_rep = !!mop->event;
         else
             rc = -EINVAL;
diff --git a/xen/include/asm-x86/vm_event.h b/xen/include/asm-x86/vm_event.h
index 026f42e..557f353 100644
--- a/xen/include/asm-x86/vm_event.h
+++ b/xen/include/asm-x86/vm_event.h
@@ -28,7 +28,7 @@
  */
 struct arch_vm_event {
     uint32_t emulate_flags;
-    struct vm_event_emul_read_data emul_read_data;
+    struct vm_event_emul_read_data *emul_read_data;
     struct monitor_write_data write_data;
 };
 
-- 
2.5.0


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