File 544e6885-x86-HVM-sanity-check-xsave-area-when-migrating-from-older-Xen.patch of Package xen.481

# Commit d7bb8e88a087690feba63ef83c13ba067f041da0
# Date 2014-10-27 16:45:09 +0100
# Author Don Koch <dkoch@verizon.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/HVM: sanity check xsave area when migrating or restoring from older Xen versions

Xen 4.3.0, 4.2.3 and older transferred a maximum sized xsave area (as
if all the available XCR0 bits were set); the new version only
transfers based on the actual XCR0 bits. This may result in a smaller
area if the last sections were missing (e.g., the LWP area from an AMD
machine). If the size doesn't match the XCR0 derived size, the size is
checked against the maximum size and the part of the xsave area
between the actual and maximum used size is checked for zero data. If
either the max size check or any part of the overflow area is
non-zero, we return with an error.

Signed-off-by: Don Koch <dkoch@verizon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1108,6 +1108,7 @@ static int hvm_load_cpu_xsave_states(str
     struct vcpu *v;
     struct hvm_hw_cpu_xsave *ctxt;
     struct hvm_save_descriptor *desc;
+    unsigned int i, desc_start;
 
     /* Which vcpu is this? */
     vcpuid = hvm_load_instance(h);
@@ -1148,15 +1149,8 @@ static int hvm_load_cpu_xsave_states(str
                         save_area) + XSTATE_AREA_MIN_SIZE);
         return -EINVAL;
     }
-    size = HVM_CPU_XSAVE_SIZE(xfeature_mask);
-    if ( desc->length > size )
-    {
-        printk(XENLOG_G_WARNING
-               "HVM%d.%d restore mismatch: xsave length %u > %u\n",
-               d->domain_id, vcpuid, desc->length, size);
-        return -EOPNOTSUPP;
-    }
     h->cur += sizeof (*desc);
+    desc_start = h->cur;
 
     ctxt = (struct hvm_hw_cpu_xsave *)&h->data[h->cur];
     h->cur += desc->length;
@@ -1176,10 +1170,24 @@ static int hvm_load_cpu_xsave_states(str
     size = HVM_CPU_XSAVE_SIZE(ctxt->xcr0_accum);
     if ( desc->length > size )
     {
+        /*
+         * Xen 4.3.0, 4.2.3 and older used to send longer-than-needed
+         * xsave regions.  Permit loading the record if the extra data
+         * is all zero.
+         */
+        for ( i = size; i < desc->length; i++ )
+        {
+            if ( h->data[desc_start + i] )
+            {
+                printk(XENLOG_G_WARNING
+                       "HVM%d.%u restore mismatch: xsave length %#x > %#x (non-zero data at %#x)\n",
+                       d->domain_id, vcpuid, desc->length, size, i);
+                return -EOPNOTSUPP;
+            }
+        }
         printk(XENLOG_G_WARNING
-               "HVM%d.%d restore mismatch: xsave length %u > %u\n",
+               "HVM%d.%u restore mismatch: xsave length %#x > %#x\n",
                d->domain_id, vcpuid, desc->length, size);
-        return -EOPNOTSUPP;
     }
     /* Checking finished */
 
@@ -1188,7 +1196,8 @@ static int hvm_load_cpu_xsave_states(str
     if ( ctxt->xcr0_accum & XSTATE_NONLAZY )
         v->arch.nonlazy_xstate_used = 1;
     memcpy(v->arch.xsave_area, &ctxt->save_area,
-           desc->length - offsetof(struct hvm_hw_cpu_xsave, save_area));
+           min(desc->length, size) - offsetof(struct hvm_hw_cpu_xsave,
+           save_area));
 
     return 0;
 }