[Xen-changelog] [xen stable-4.2] x86: make page table unpinning preemptible

[patchbot@xxxxxxx]

commit 3e5c1c0093013a4274124eee7862f8e41021b220
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu May 2 17:18:28 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu May 2 17:18:28 2013 +0200

    x86: make page table unpinning preemptible
    
    ... as it may take significant amounts of time.
    
    Since we can't re-invoke the operation in a second attempt, the
    continuation logic must be slightly tweaked so that we make sure
    do_mmuext_op() gets run one more time even when the preempted unpin
    operation was the last one in a batch.
    
    This is part of CVE-2013-1918 / XSA-45.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
    master commit: a3e049f8e86fe18e3b87f18dc0c7be665026fd9f
    master date: 2013-05-02 16:39:06 +0200
---
 xen/arch/x86/mm.c               |   40 +++++++++++++++++++++++++++++++++++++-
 xen/arch/x86/x86_64/compat/mm.c |   23 +++++++++++++++++----
 2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 8ca4fda..5d5a15e 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3123,6 +3123,14 @@ long do_mmuext_op(
         return rc;
     }
 
+    if ( unlikely(count == MMU_UPDATE_PREEMPTED) &&
+         likely(guest_handle_is_null(uops)) )
+    {
+        /* See the curr->arch.old_guest_table related
+         * hypercall_create_continuation() below. */
+        return (int)foreigndom;
+    }
+
     if ( unlikely(count & MMU_UPDATE_PREEMPTED) )
     {
         count &= ~MMU_UPDATE_PREEMPTED;
@@ -3146,7 +3154,7 @@ long do_mmuext_op(
 
     for ( i = 0; i < count; i++ )
     {
-        if ( hypercall_preempt_check() )
+        if ( curr->arch.old_guest_table || hypercall_preempt_check() )
         {
             rc = -EAGAIN;
             break;
@@ -3266,7 +3274,17 @@ long do_mmuext_op(
                 break;
             }
 
-            put_page_and_type(page);
+            switch ( rc = put_page_and_type_preemptible(page, 1) )
+            {
+            case -EINTR:
+            case -EAGAIN:
+                curr->arch.old_guest_table = page;
+                rc = 0;
+                break;
+            default:
+                BUG_ON(rc);
+                break;
+            }
             put_page(page);
 
             /* A page is dirtied when its pin status is cleared. */
@@ -3587,9 +3605,27 @@ long do_mmuext_op(
     }
 
     if ( rc == -EAGAIN )
+    {
+        ASSERT(i < count);
         rc = hypercall_create_continuation(
             __HYPERVISOR_mmuext_op, "hihi",
             uops, (count - i) | MMU_UPDATE_PREEMPTED, pdone, foreigndom);
+    }
+    else if ( curr->arch.old_guest_table )
+    {
+        XEN_GUEST_HANDLE(void) null;
+
+        ASSERT(rc || i == count);
+        set_xen_guest_handle(null, NULL);
+        /*
+         * In order to have a way to communicate the final return value to
+         * our continuation, we pass this in place of "foreigndom", building
+         * on the fact that this argument isn't needed anymore.
+         */
+        rc = hypercall_create_continuation(
+                __HYPERVISOR_mmuext_op, "hihi", null,
+                MMU_UPDATE_PREEMPTED, null, rc);
+    }
 
     put_pg_owner(pg_owner);
 
diff --git a/xen/arch/x86/x86_64/compat/mm.c b/xen/arch/x86/x86_64/compat/mm.c
index ce662a5..ef7822b 100644
--- a/xen/arch/x86/x86_64/compat/mm.c
+++ b/xen/arch/x86/x86_64/compat/mm.c
@@ -268,6 +268,13 @@ int compat_mmuext_op(XEN_GUEST_HANDLE(mmuext_op_compat_t) 
cmp_uops,
     int rc = 0;
     XEN_GUEST_HANDLE(mmuext_op_t) nat_ops;
 
+    if ( unlikely(count == MMU_UPDATE_PREEMPTED) &&
+         likely(guest_handle_is_null(cmp_uops)) )
+    {
+        set_xen_guest_handle(nat_ops, NULL);
+        return do_mmuext_op(nat_ops, count, pdone, foreigndom);
+    }
+
     preempt_mask = count & MMU_UPDATE_PREEMPTED;
     count ^= preempt_mask;
 
@@ -370,12 +377,18 @@ int compat_mmuext_op(XEN_GUEST_HANDLE(mmuext_op_compat_t) 
cmp_uops,
                 guest_handle_add_offset(nat_ops, i - left);
                 guest_handle_subtract_offset(cmp_uops, left);
                 left = 1;
-                BUG_ON(!hypercall_xlat_continuation(&left, 0x01, nat_ops, 
cmp_uops));
-                BUG_ON(left != arg1);
-                if (!test_bit(_MCSF_in_multicall, &mcs->flags))
-                    regs->_ecx += count - i;
+                if ( arg1 != MMU_UPDATE_PREEMPTED )
+                {
+                    BUG_ON(!hypercall_xlat_continuation(&left, 0x01, nat_ops,
+                                                        cmp_uops));
+                    if ( !test_bit(_MCSF_in_multicall, &mcs->flags) )
+                        regs->_ecx += count - i;
+                    else
+                        mcs->compat_call.args[1] += count - i;
+                }
                 else
-                    mcs->compat_call.args[1] += count - i;
+                    BUG_ON(hypercall_xlat_continuation(&left, 0));
+                BUG_ON(left != arg1);
             }
             else
                 BUG_ON(err > 0);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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