References: CVE-2012-5511 XSA-27 bnc#789944

hvm: Limit the size of large HVM op batches

Doing large p2m updates for HVMOP_track_dirty_vram without preemption
ties up the physical processor. Integrating preemption into the p2m
updates is hard so simply limit to 1GB which is sufficient for a 15000
* 15000 * 32bpp framebuffer.

For HVMOP_modified_memory and HVMOP_set_mem_type preemptible add the
necessary machinery to handle preemption.

This is CVE-2012-5511 / XSA-27.

Signed-off-by: Tim Deegan <tim@xen.org>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

v2: Provide definition of GB to fix x86-32 compile.

Signed-off-by: Jan Beulich <JBeulich@suse.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>


--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4033,6 +4033,9 @@ long do_hvm_op(unsigned long op, XEN_GUE
         if ( !is_hvm_domain(d) )
             goto param_fail2;
 
+        if ( a.nr > GB(1) >> PAGE_SHIFT )
+            goto param_fail2;
+
         rc = xsm_hvm_param(d, op);
         if ( rc )
             goto param_fail2;
@@ -4059,7 +4062,6 @@ long do_hvm_op(unsigned long op, XEN_GUE
     {
         struct xen_hvm_modified_memory a;
         struct domain *d;
-        unsigned long pfn;
 
         if ( copy_from_guest(&a, arg, 1) )
             return -EFAULT;
@@ -4086,9 +4088,11 @@ long do_hvm_op(unsigned long op, XEN_GUE
         if ( !paging_mode_log_dirty(d) )
             goto param_fail3;
 
-        for ( pfn = a.first_pfn; pfn < a.first_pfn + a.nr; pfn++ )
+        while ( a.nr > 0 )
         {
+            unsigned long pfn = a.first_pfn;
             struct page_info *page;
+
             page = get_page_from_gfn(d, pfn, NULL, P2M_UNSHARE);
             if ( page )
             {
@@ -4098,6 +4102,19 @@ long do_hvm_op(unsigned long op, XEN_GUE
                 sh_remove_shadows(d->vcpu[0], _mfn(page_to_mfn(page)), 1, 0);
                 put_page(page);
             }
+
+            a.first_pfn++;
+            a.nr--;
+
+            /* Check for continuation if it's not the last interation */
+            if ( a.nr > 0 && hypercall_preempt_check() )
+            {
+                if ( copy_to_guest(arg, &a, 1) )
+                    rc = -EFAULT;
+                else
+                    rc = -EAGAIN;
+                break;
+            }
         }
 
     param_fail3:
@@ -4153,7 +4170,6 @@ long do_hvm_op(unsigned long op, XEN_GUE
     {
         struct xen_hvm_set_mem_type a;
         struct domain *d;
-        unsigned long pfn;
         
         /* Interface types to internal p2m types */
         p2m_type_t memtype[] = {
@@ -4186,8 +4202,9 @@ long do_hvm_op(unsigned long op, XEN_GUE
         if ( a.hvmmem_type >= ARRAY_SIZE(memtype) )
             goto param_fail4;
 
-        for ( pfn = a.first_pfn; pfn < a.first_pfn + a.nr; pfn++ )
+        while ( a.nr )
         {
+            unsigned long pfn = a.first_pfn;
             p2m_type_t t;
             p2m_type_t nt;
             mfn_t mfn;
@@ -4227,6 +4244,19 @@ long do_hvm_op(unsigned long op, XEN_GUE
                 }
             }
             put_gfn(d, pfn);
+
+            a.first_pfn++;
+            a.nr--;
+
+            /* Check for continuation if it's not the last interation */
+            if ( a.nr > 0 && hypercall_preempt_check() )
+            {
+                if ( copy_to_guest(arg, &a, 1) )
+                    rc = -EFAULT;
+                else
+                    rc = -EAGAIN;
+                goto param_fail4;
+            }
         }
 
         rc = 0;
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -119,6 +119,9 @@ extern char wakeup_start[];
 extern unsigned int video_mode, video_flags;
 extern unsigned short boot_edid_caps;
 extern unsigned char boot_edid_info[128];
+
+#define GB(_gb) (_gb ## UL << 30)
+
 #endif
 
 #define asmlinkage
@@ -134,7 +137,6 @@ extern unsigned char boot_edid_info[128]
 #define PML4_ADDR(_slot)                             \
     ((((_slot ## UL) >> 8) * 0xffff000000000000UL) | \
      (_slot ## UL << PML4_ENTRY_BITS))
-#define GB(_gb) (_gb ## UL << 30)
 #else
 #define PML4_ENTRY_BYTES (1 << PML4_ENTRY_BITS)
 #define PML4_ADDR(_slot)                             \