x86/paging: make log-dirty operations preemptible

Both the freeing and the inspection of the bitmap get done in (nested)
loops which - besides having a rather high iteration count in general,
albeit that would be covered by XSA-77 - have the number of non-trivial
iterations they need to perform (indirectly) controllable by both the
guest they are for and any domain controlling the guest (including the
one running qemu for it).

This is CVE-2014-5146 / XSA-97.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
master commit: 95e6d82224689fdfd967a093a4d69efc24c17e91
master date: 2014-08-12 15:30:11 +0200

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 8f11473afe85149da4366ea32f9bbdb4ba828100..2799e8618ca0319d96bebf2545137f546e5e95bf 100644 (file)
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -2136,7 +2136,9 @@ int domain_relinquish_resources(struct domain *d)
         pci_release_devices(d);
 
         /* Tear down paging-assistance stuff. */
-        paging_teardown(d);
+        ret = paging_teardown(d);
+        if ( ret )
+            return ret;
 
         /* Drop the in-use references to page-table bases. */
         for_each_vcpu ( d, v )

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 48de4bfc86cf7f280987061ed128668dc2bd0eac..e392cca5c61e36f61cc32923c0887ef309ec29f5 100644 (file)
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -66,6 +66,9 @@ long arch_do_domctl(
                                 &domctl->u.shadow_op,
                                 guest_handle_cast(u_domctl, void));
             rcu_unlock_domain(d);
+            if ( ret == -EAGAIN )
+                return hypercall_create_continuation(__HYPERVISOR_domctl,
+                                                     "h", u_domctl);
             copy_to_guest(u_domctl, domctl, 1);
         } 
     }

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index c198323c5aacfc4ffb1bfebe704c4c9740ca209c..acdc192f88fa9f53bd940e08efa8e1589274a382 100644 (file)
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -678,8 +678,7 @@ int hap_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
         paging_unlock(d);
         if ( preempted )
             /* Not finished.  Set up to re-run the call. */
-            rc = hypercall_create_continuation(__HYPERVISOR_domctl, "h",
-                                               u_domctl);
+            rc = -EAGAIN;
         else
             /* Finished.  Return the new allocation */
             sc->mb = hap_get_allocation(d);

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 0fd1199ea3ed592d041943022930404271de1152..7a7fdf6f548234506edce4c7bd77d93fce5d57d2 100644 (file)
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -26,6 +26,7 @@
 #include <asm/shadow.h>
 #include <asm/p2m.h>
 #include <asm/hap.h>
+#include <asm/event.h>
 #include <asm/hvm/nestedhvm.h>
 #include <xen/numa.h>
 #include <xsm/xsm.h>
@@ -116,26 +117,46 @@ static void paging_free_log_dirty_page(struct domain *d, mfn_t mfn)
     d->arch.paging.free_page(d, mfn_to_page(mfn));
 }
 
-void paging_free_log_dirty_bitmap(struct domain *d)
+static int paging_free_log_dirty_bitmap(struct domain *d, int rc)
 {
     mfn_t *l4, *l3, *l2;
     int i4, i3, i2;
 
+    paging_lock(d);
+
     if ( !mfn_valid(d->arch.paging.log_dirty.top) )
-        return;
+    {
+        paging_unlock(d);
+        return 0;
+    }
 
-    paging_lock(d);
+    if ( !d->arch.paging.preempt.vcpu )
+    {
+        memset(&d->arch.paging.preempt.log_dirty, 0,
+               sizeof(d->arch.paging.preempt.log_dirty));
+        ASSERT(rc <= 0);
+        d->arch.paging.preempt.log_dirty.done = -rc;
+    }
+    else if ( d->arch.paging.preempt.vcpu != current ||
+              d->arch.paging.preempt.op != XEN_DOMCTL_SHADOW_OP_OFF )
+    {
+        paging_unlock(d);
+        return -EBUSY;
+    }
 
     l4 = map_domain_page(mfn_x(d->arch.paging.log_dirty.top));
+    i4 = d->arch.paging.preempt.log_dirty.i4;
+    i3 = d->arch.paging.preempt.log_dirty.i3;
+    rc = 0;
 
-    for ( i4 = 0; i4 < LOGDIRTY_NODE_ENTRIES; i4++ )
+    for ( ; i4 < LOGDIRTY_NODE_ENTRIES; i4++, i3 = 0 )
     {
         if ( !mfn_valid(l4[i4]) )
             continue;
 
         l3 = map_domain_page(mfn_x(l4[i4]));
 
-        for ( i3 = 0; i3 < LOGDIRTY_NODE_ENTRIES; i3++ )
+        for ( ; i3 < LOGDIRTY_NODE_ENTRIES; i3++ )
         {
             if ( !mfn_valid(l3[i3]) )
                 continue;
@@ -148,20 +169,54 @@ void paging_free_log_dirty_bitmap(struct domain *d)
 
             unmap_domain_page(l2);
             paging_free_log_dirty_page(d, l3[i3]);
+            l3[i3] = _mfn(INVALID_MFN);
+
+            if ( i3 < LOGDIRTY_NODE_ENTRIES - 1 && hypercall_preempt_check() )
+            {
+                d->arch.paging.preempt.log_dirty.i3 = i3 + 1;
+                d->arch.paging.preempt.log_dirty.i4 = i4;
+                rc = -EAGAIN;
+                break;
+            }
         }
 
         unmap_domain_page(l3);
+        if ( rc )
+            break;
         paging_free_log_dirty_page(d, l4[i4]);
+        l4[i4] = _mfn(INVALID_MFN);
+
+        if ( i4 < LOGDIRTY_NODE_ENTRIES - 1 && hypercall_preempt_check() )
+        {
+            d->arch.paging.preempt.log_dirty.i3 = 0;
+            d->arch.paging.preempt.log_dirty.i4 = i4 + 1;
+            rc = -EAGAIN;
+            break;
+        }
     }
 
     unmap_domain_page(l4);
-    paging_free_log_dirty_page(d, d->arch.paging.log_dirty.top);
-    d->arch.paging.log_dirty.top = _mfn(INVALID_MFN);
 
-    ASSERT(d->arch.paging.log_dirty.allocs == 0);
-    d->arch.paging.log_dirty.failed_allocs = 0;
+    if ( !rc )
+    {
+        paging_free_log_dirty_page(d, d->arch.paging.log_dirty.top);
+        d->arch.paging.log_dirty.top = _mfn(INVALID_MFN);
+
+        ASSERT(d->arch.paging.log_dirty.allocs == 0);
+        d->arch.paging.log_dirty.failed_allocs = 0;
+
+        rc = -d->arch.paging.preempt.log_dirty.done;
+        d->arch.paging.preempt.vcpu = NULL;
+    }
+    else
+    {
+        d->arch.paging.preempt.vcpu = current;
+        d->arch.paging.preempt.op = XEN_DOMCTL_SHADOW_OP_OFF;
+    }
 
     paging_unlock(d);
+
+    return rc;
 }
 
 int paging_log_dirty_enable(struct domain *d)
@@ -178,15 +233,25 @@ int paging_log_dirty_enable(struct domain *d)
     return ret;
 }
 
-int paging_log_dirty_disable(struct domain *d)
+static int paging_log_dirty_disable(struct domain *d, bool_t resuming)
 {
-    int ret;
+    int ret = 1;
+
+    if ( !resuming )
+    {
+        domain_pause(d);
+        /* Safe because the domain is paused. */
+        ret = d->arch.paging.log_dirty.disable_log_dirty(d);
+        ASSERT(ret <= 0);
+    }
 
-    domain_pause(d);
-    /* Safe because the domain is paused. */
-    ret = d->arch.paging.log_dirty.disable_log_dirty(d);
     if ( !paging_mode_log_dirty(d) )
-        paging_free_log_dirty_bitmap(d);
+    {
+        ret = paging_free_log_dirty_bitmap(d, ret);
+        if ( ret == -EAGAIN )
+            return ret;
+    }
+
     domain_unpause(d);
 
     return ret;
@@ -326,7 +391,9 @@ int paging_mfn_is_dirty(struct domain *d, mfn_t gmfn)
 
 /* Read a domain's log-dirty bitmap and stats.  If the operation is a CLEAN,
  * clear the bitmap and stats as well. */
-int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
+static int paging_log_dirty_op(struct domain *d,
+                               struct xen_domctl_shadow_op *sc,
+                               bool_t resuming)
 {
     int rv = 0, clean = 0, peek = 1;
     unsigned long pages = 0;
@@ -334,9 +401,22 @@ int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
     unsigned long *l1 = NULL;
     int i4, i3, i2;
 
-    domain_pause(d);
+    if ( !resuming )
+        domain_pause(d);
     paging_lock(d);
 
+    if ( !d->arch.paging.preempt.vcpu )
+        memset(&d->arch.paging.preempt.log_dirty, 0,
+               sizeof(d->arch.paging.preempt.log_dirty));
+    else if ( d->arch.paging.preempt.vcpu != current ||
+              d->arch.paging.preempt.op != sc->op )
+    {
+        paging_unlock(d);
+        ASSERT(!resuming);
+        domain_unpause(d);
+        return -EBUSY;
+    }
+
     clean = (sc->op == XEN_DOMCTL_SHADOW_OP_CLEAN);
 
     PAGING_DEBUG(LOGDIRTY, "log-dirty %s: dom %u faults=%u dirty=%u\n",
@@ -365,17 +445,15 @@ int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
         goto out;
     }
 
-    pages = 0;
     l4 = paging_map_log_dirty_bitmap(d);
+    i4 = d->arch.paging.preempt.log_dirty.i4;
+    i3 = d->arch.paging.preempt.log_dirty.i3;
+    pages = d->arch.paging.preempt.log_dirty.done;
 
-    for ( i4 = 0;
-          (pages < sc->pages) && (i4 < LOGDIRTY_NODE_ENTRIES);
-          i4++ )
+    for ( ; (pages < sc->pages) && (i4 < LOGDIRTY_NODE_ENTRIES); i4++, i3 = 0 )
     {
         l3 = (l4 && mfn_valid(l4[i4])) ? map_domain_page(mfn_x(l4[i4])) : NULL;
-        for ( i3 = 0;
-              (pages < sc->pages) && (i3 < LOGDIRTY_NODE_ENTRIES);
-              i3++ )
+        for ( ; (pages < sc->pages) && (i3 < LOGDIRTY_NODE_ENTRIES); i3++ )
         {
             l2 = ((l3 && mfn_valid(l3[i3])) ?
                   map_domain_page(mfn_x(l3[i3])) : NULL);
@@ -410,18 +488,51 @@ int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
             }
             if ( l2 )
                 unmap_domain_page(l2);
+
+            if ( i3 < LOGDIRTY_NODE_ENTRIES - 1 && hypercall_preempt_check() )
+            {
+                d->arch.paging.preempt.log_dirty.i4 = i4;
+                d->arch.paging.preempt.log_dirty.i3 = i3 + 1;
+                rv = -EAGAIN;
+                break;
+            }
         }
         if ( l3 )
             unmap_domain_page(l3);
+
+        if ( !rv && i4 < LOGDIRTY_NODE_ENTRIES - 1 &&
+             hypercall_preempt_check() )
+        {
+            d->arch.paging.preempt.log_dirty.i4 = i4 + 1;
+            d->arch.paging.preempt.log_dirty.i3 = 0;
+            rv = -EAGAIN;
+        }
+        if ( rv )
+            break;
     }
     if ( l4 )
         unmap_domain_page(l4);
 
-    if ( pages < sc->pages )
-        sc->pages = pages;
+    if ( !rv )
+        d->arch.paging.preempt.vcpu = NULL;
+    else
+    {
+        d->arch.paging.preempt.vcpu = current;
+        d->arch.paging.preempt.op = sc->op;
+        d->arch.paging.preempt.log_dirty.done = pages;
+    }
 
     paging_unlock(d);
 
+    if ( rv )
+    {
+        /* Never leave the domain paused for other errors. */
+        ASSERT(rv == -EAGAIN);
+        return rv;
+    }
+
+    if ( pages < sc->pages )
+        sc->pages = pages;
     if ( clean )
     {
         /* We need to further call clean_dirty_bitmap() functions of specific
@@ -432,6 +543,7 @@ int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
     return rv;
 
  out:
+    d->arch.paging.preempt.vcpu = NULL;
     paging_unlock(d);
     domain_unpause(d);
 
@@ -498,12 +610,6 @@ void paging_log_dirty_init(struct domain *d,
     d->arch.paging.log_dirty.clean_dirty_bitmap = clean_dirty_bitmap;
 }
 
-/* This function fress log dirty bitmap resources. */
-static void paging_log_dirty_teardown(struct domain*d)
-{
-    paging_free_log_dirty_bitmap(d);
-}
-
 /************************************************/
 /*           CODE FOR PAGING SUPPORT            */
 /************************************************/
@@ -547,6 +653,7 @@ void paging_vcpu_init(struct vcpu *v)
 int paging_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
                   XEN_GUEST_HANDLE(void) u_domctl)
 {
+    bool_t resuming = 0;
     int rc;
 
     if ( unlikely(d == current->domain) )
@@ -569,6 +676,20 @@ int paging_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
         return -EINVAL;
     }
 
+    if ( d->arch.paging.preempt.vcpu )
+    {
+        if ( d->arch.paging.preempt.vcpu != current ||
+             d->arch.paging.preempt.op != sc->op )
+        {
+            printk(XENLOG_G_DEBUG
+                   "d%d:v%d: Paging op %#x on Dom%u with unfinished prior op %#x\n",
+                   current->domain->domain_id, current->vcpu_id,
+                   sc->op, d->domain_id, d->arch.paging.preempt.op);
+            return -EBUSY;
+        }
+        resuming = 1;
+    }
+
     rc = xsm_shadow_control(d, sc->op);
     if ( rc )
         return rc;
@@ -594,13 +715,13 @@ int paging_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
 
     case XEN_DOMCTL_SHADOW_OP_OFF:
         if ( paging_mode_log_dirty(d) )
-            if ( (rc = paging_log_dirty_disable(d)) != 0 )
+            if ( (rc = paging_log_dirty_disable(d, resuming)) != 0 )
                 return rc;
         break;
 
     case XEN_DOMCTL_SHADOW_OP_CLEAN:
     case XEN_DOMCTL_SHADOW_OP_PEEK:
-        return paging_log_dirty_op(d, sc);
+        return paging_log_dirty_op(d, sc, resuming);
     }
 
     /* Here, dispatch domctl to the appropriate paging code */
@@ -611,18 +732,24 @@ int paging_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
 }
 
 /* Call when destroying a domain */
-void paging_teardown(struct domain *d)
+int paging_teardown(struct domain *d)
 {
+    int rc;
+
     if ( hap_enabled(d) )
         hap_teardown(d);
     else
         shadow_teardown(d);
 
     /* clean up log dirty resources. */
-    paging_log_dirty_teardown(d);
+    rc = paging_free_log_dirty_bitmap(d, 0);
+    if ( rc == -EAGAIN )
+        return rc;
 
     /* Move populate-on-demand cache back to domain_list for destruction */
     p2m_pod_empty_cache(d);
+
+    return rc;
 }
 
 /* Call once all of the references to the domain have gone away */

diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 0362c859d795ff03bc55412a7a971c91bac0758e..d5c59057be06e46bf9d9f4b30150a86bbde41f2c 100644 (file)
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3829,8 +3829,7 @@ int shadow_domctl(struct domain *d,
         paging_unlock(d);
         if ( preempted )
             /* Not finished.  Set up to re-run the call. */
-            rc = hypercall_create_continuation(
-                __HYPERVISOR_domctl, "h", u_domctl);
+            rc = -EAGAIN;
         else 
             /* Finished.  Return the new allocation */
             sc->mb = shadow_get_allocation(d);

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 73842f9312977e41d88b12a4ba791e8183b9f471..45d90bf167f0e9306e0accb9ef08fae6c134dea1 100644 (file)
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -479,7 +479,6 @@ int domain_kill(struct domain *d)
         rc = domain_relinquish_resources(d);
         if ( rc != 0 )
         {
-            BUG_ON(rc != -EAGAIN);
             break;
         }
         if ( sched_move_domain(d, cpupool0) )

diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 6c62c2594a91e7f81ebc66e7720cc3b9ee7b256f..bd170ed7850a1ee4418c7a5ea165cc46cdffba01 100644 (file)
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -193,6 +193,20 @@ struct paging_domain {
     struct hap_domain       hap;
     /* log dirty support */
     struct log_dirty_domain log_dirty;
+
+    /* preemption handling */
+    struct {
+        struct vcpu *vcpu;
+        unsigned int op;
+        union {
+            struct {
+                unsigned long done:PADDR_BITS - PAGE_SHIFT;
+                unsigned long i4:PAGETABLE_ORDER;
+                unsigned long i3:PAGETABLE_ORDER;
+            } log_dirty;
+        };
+    } preempt;
+
     /* alloc/free pages from the pool for paging-assistance structures
      * (used by p2m and log-dirty code for their tries) */
     struct page_info * (*alloc_page)(struct domain *d);

diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index 1e77e781e723a91f1d58d558cff957efbe01d977..21daf0418cc82acf5a8b0511e64157b324e7d196 100644 (file)
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -141,9 +141,6 @@ struct paging_mode {
 /*****************************************************************************
  * Log dirty code */
 
-/* free log dirty bitmap resource */
-void paging_free_log_dirty_bitmap(struct domain *d);
-
 /* get the dirty bitmap for a specific range of pfns */
 void paging_log_dirty_range(struct domain *d,
                             unsigned long begin_pfn,
@@ -153,9 +150,6 @@ void paging_log_dirty_range(struct domain *d,
 /* enable log dirty */
 int paging_log_dirty_enable(struct domain *d);
 
-/* disable log dirty */
-int paging_log_dirty_disable(struct domain *d);
-
 /* log dirty initialization */
 void paging_log_dirty_init(struct domain *d,
                            int  (*enable_log_dirty)(struct domain *d),
@@ -218,7 +212,7 @@ int paging_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
                   XEN_GUEST_HANDLE(void) u_domctl);
 
 /* Call when destroying a domain */
-void paging_teardown(struct domain *d);
+int paging_teardown(struct domain *d);
 
 /* Call once all of the references to the domain have gone away */
 void paging_final_teardown(struct domain *d);