[Xen-changelog] [xen master] x86: fix page refcount handling in page table pin error path

[patchbot@xxxxxxx]

commit 9b167bd2f394f821ae3252d74a15704a4bf91f6d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Jun 26 15:32:58 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jun 26 15:32:58 2013 +0200

    x86: fix page refcount handling in page table pin error path
    
    In the original patch 7 of the series addressing XSA-45 I mistakenly
    took the addition of the call to get_page_light() in alloc_page_type()
    to cover two decrements that would happen: One for the PGT_partial bit
    that is getting set along with the call, and the other for the page
    reference the caller hold (and would be dropping on its error path).
    But of course the additional page reference is tied to the PGT_partial
    bit, and hence any caller of a function that may leave
    ->arch.old_guest_table non-NULL for error cleanup purposes has to make
    sure a respective page reference gets retained.
    
    Similar issues were then also spotted elsewhere: In effect all callers
    of get_page_type_preemptible() need to deal with errors in similar
    ways. To make sure error handling can work this way without leaking
    page references, a respective assertion gets added to that function.
    
    This is CVE-2013-1432 / XSA-58.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/domain.c    |   27 +++++++++++++++++++++------
 xen/arch/x86/mm.c        |    9 ++++++---
 xen/include/asm-x86/mm.h |    1 +
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 48f3487..52c9040 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -829,6 +829,10 @@ int arch_set_info_guest(
     if ( v->vcpu_id == 0 )
         d->vm_assist = c(vm_assist);
 
+    rc = put_old_guest_table(current);
+    if ( rc )
+        return rc;
+
     if ( !compat )
         rc = (int)set_gdt(v, c.nat->gdt_frames, c.nat->gdt_ents);
     else
@@ -864,18 +868,24 @@ int arch_set_info_guest(
     }
     else
     {
-        /*
-         * Since v->arch.guest_table{,_user} are both NULL, this effectively
-         * is just a call to put_old_guest_table().
-         */
         if ( !compat )
-            rc = vcpu_destroy_pagetables(v);
+            rc = put_old_guest_table(v);
         if ( !rc )
             rc = get_page_type_preemptible(cr3_page,
                                            !compat ? PGT_root_page_table
                                                    : PGT_l3_page_table);
-        if ( rc == -EINTR )
+        switch ( rc )
+        {
+        case -EINTR:
             rc = -EAGAIN;
+        case -EAGAIN:
+        case 0:
+            break;
+        default:
+            if ( cr3_page == current->arch.old_guest_table )
+                cr3_page = NULL;
+            break;
+        }
     }
     if ( rc )
         /* handled below */;
@@ -901,6 +911,11 @@ int arch_set_info_guest(
                         pagetable_get_page(v->arch.guest_table);
                     v->arch.guest_table = pagetable_null();
                     break;
+                default:
+                    if ( cr3_page == current->arch.old_guest_table )
+                        cr3_page = NULL;
+                case 0:
+                    break;
                 }
             }
             if ( !rc )
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 5123860..77dcafc 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -640,7 +640,8 @@ static int get_page_and_type_from_pagenr(unsigned long 
page_nr,
           get_page_type_preemptible(page, type) :
           (get_page_type(page, type) ? 0 : -EINVAL));
 
-    if ( unlikely(rc) && partial >= 0 )
+    if ( unlikely(rc) && partial >= 0 &&
+         (!preemptible || page != current->arch.old_guest_table) )
         put_page(page);
 
     return rc;
@@ -2427,6 +2428,7 @@ int put_page_type_preemptible(struct page_info *page)
 
 int get_page_type_preemptible(struct page_info *page, unsigned long type)
 {
+    ASSERT(!current->arch.old_guest_table);
     return __get_page_type(page, type, 1);
 }
 
@@ -2617,7 +2619,7 @@ static void put_superpage(unsigned long mfn)
     return;
 }
 
-static int put_old_guest_table(struct vcpu *v)
+int put_old_guest_table(struct vcpu *v)
 {
     int rc;
 
@@ -2988,7 +2990,8 @@ long do_mmuext_op(
                     rc = -EAGAIN;
                 else if ( rc != -EAGAIN )
                     MEM_LOG("Error while pinning mfn %lx", page_to_mfn(page));
-                put_page(page);
+                if ( page != curr->arch.old_guest_table )
+                    put_page(page);
                 break;
             }
 
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 6b367c0..213fc9c 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -354,6 +354,7 @@ void put_page_type(struct page_info *page);
 int  get_page_type(struct page_info *page, unsigned long type);
 int  put_page_type_preemptible(struct page_info *page);
 int  get_page_type_preemptible(struct page_info *page, unsigned long type);
+int  put_old_guest_table(struct vcpu *);
 int  get_page_from_l1e(
     l1_pgentry_t l1e, struct domain *l1e_owner, struct domain *pg_owner);
 void put_page_from_l1e(l1_pgentry_t l1e, struct domain *l1e_owner);
--
generated by git-patchbot for /home/xen/git/xen.git#master

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