# Commit c612481d1c9232c6abf91b03ec655e92f808805f
# Date 2018-08-14 16:56:47 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/mm: Plumbing to allow any PTE update to fail with -EAGAIN

Switching to shadow mode is performed in tasklet context.  To facilitate this,
we schedule the tasklet, then create a hypercall continuation to allow the
switch to take place.

As a consequence, the x86 mm code needs to cope with an L1e operation being
continuable.  do_mmu{,ext}_op() may no longer assert that a continuation
doesn't happen on the final iteration.

To handle the arguments correctly on continuation, compat_update_va_mapping*()
may no longer call into their non-compat counterparts.  Move the compat
functions into mm.c rather than exporting __do_update_va_mapping() and
{get,put}_pg_owner(), and fix an unsigned long/int inconsistency with
compat_update_va_mapping_otherdomain().

This is part of XSA-273 / CVE-2018-3620.

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

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -724,6 +724,8 @@ static int get_page_from_pagenr(unsigned
     return 1;
 }
 
+static int __get_page_type(struct page_info *page, unsigned long type,
+                           int preemptible);
 
 static int get_page_and_type_from_pagenr(unsigned long page_nr, 
                                          unsigned long type,
@@ -738,9 +740,7 @@ static int get_page_and_type_from_pagenr
          unlikely(!get_page_from_pagenr(page_nr, d)) )
         return -EINVAL;
 
-    rc = (preemptible ?
-          get_page_type_preemptible(page, type) :
-          (get_page_type(page, type) ? 0 : -EINVAL));
+    rc = __get_page_type(page, type, preemptible);
 
     if ( unlikely(rc) && partial >= 0 &&
          (!preemptible || page != current->arch.old_guest_table) )
@@ -1614,8 +1614,7 @@ static void pae_flush_pgd(
 # define pae_flush_pgd(mfn, idx, nl3e) ((void)0)
 #endif
 
-static int alloc_l2_table(struct page_info *page, unsigned long type,
-                          int preemptible)
+static int alloc_l2_table(struct page_info *page, unsigned long type)
 {
     struct domain *d = page_get_owner(page);
     unsigned long  pfn = page_to_mfn(page);
@@ -1627,8 +1626,7 @@ static int alloc_l2_table(struct page_in
 
     for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ )
     {
-        if ( preemptible && i > page->nr_validated_ptes
-             && hypercall_preempt_check() )
+        if ( i > page->nr_validated_ptes && hypercall_preempt_check() )
         {
             page->nr_validated_ptes = i;
             rc = -EAGAIN;
@@ -1639,6 +1637,12 @@ static int alloc_l2_table(struct page_in
              (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 )
             continue;
 
+        if ( unlikely(rc == -EAGAIN) )
+        {
+            page->nr_validated_ptes = i;
+            break;
+        }
+
         if ( rc < 0 )
         {
             MEM_LOG("Failure in alloc_l2_table: entry %d", i);
@@ -1850,7 +1854,7 @@ static void free_l1_table(struct page_in
 }
 
 
-static int free_l2_table(struct page_info *page, int preemptible)
+static int free_l2_table(struct page_info *page)
 {
 #ifdef __x86_64__
     struct domain *d = page_get_owner(page);
@@ -1866,7 +1870,7 @@ static int free_l2_table(struct page_inf
     do {
         if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) &&
              put_page_from_l2e(pl2e[i], pfn) == 0 &&
-             preemptible && i && hypercall_preempt_check() )
+             i && hypercall_preempt_check() )
         {
            page->nr_validated_ptes = i;
            err = -EAGAIN;
@@ -2450,7 +2454,8 @@ static int alloc_page_type(struct page_i
         rc = alloc_l1_table(page);
         break;
     case PGT_l2_page_table:
-        rc = alloc_l2_table(page, type, preemptible);
+        ASSERT(preemptible);
+        rc = alloc_l2_table(page, type);
         break;
     case PGT_l3_page_table:
         ASSERT(preemptible);
@@ -2545,7 +2550,8 @@ int free_page_type(struct page_info *pag
         rc = 0;
         break;
     case PGT_l2_page_table:
-        rc = free_l2_table(page, preemptible);
+        ASSERT(preemptible);
+        rc = free_l2_table(page);
         break;
     case PGT_l3_page_table:
 #if CONFIG_PAGING_LEVELS == 3
@@ -3866,12 +3872,9 @@ 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;
@@ -4180,12 +4183,9 @@ long do_mmu_update(
     }
 
     if ( rc == -EAGAIN )
-    {
-        ASSERT(i < count);
         rc = hypercall_create_continuation(
             __HYPERVISOR_mmu_update, "hihi",
             ureqs, (count - i) | MMU_UPDATE_PREEMPTED, pdone, foreigndom);
-    }
     else if ( curr->arch.old_guest_table )
     {
         XEN_GUEST_HANDLE(void) null;
@@ -4896,7 +4896,13 @@ static int __do_update_va_mapping(
 long do_update_va_mapping(unsigned long va, u64 val64,
                           unsigned long flags)
 {
-    return __do_update_va_mapping(va, val64, flags, current->domain);
+    int rc = __do_update_va_mapping(va, val64, flags, current->domain);
+
+    if ( rc == -EAGAIN )
+        rc = hypercall_create_continuation(
+            __HYPERVISOR_update_va_mapping, "lll", va, val64, flags);
+
+    return rc;
 }
 
 long do_update_va_mapping_otherdomain(unsigned long va, u64 val64,
@@ -4913,6 +4919,46 @@ long do_update_va_mapping_otherdomain(un
 
     put_pg_owner(pg_owner);
 
+    if ( rc == -EAGAIN )
+        rc = hypercall_create_continuation(
+            __HYPERVISOR_update_va_mapping_otherdomain,
+            "llli", va, val64, flags, domid);
+
+    return rc;
+}
+
+int compat_update_va_mapping(unsigned int va, uint32_t lo, uint32_t hi,
+                             unsigned int flags)
+{
+    int rc = __do_update_va_mapping(va, ((uint64_t)hi << 32) | lo,
+                                    flags, current->domain);
+
+    if ( rc == -EAGAIN )
+        rc = hypercall_create_continuation(
+            __HYPERVISOR_update_va_mapping, "iiii", va, lo, hi, flags);
+
+    return rc;
+}
+
+int compat_update_va_mapping_otherdomain(unsigned int va,
+                                         uint32_t lo, uint32_t hi,
+                                         unsigned int flags, domid_t domid)
+{
+    struct domain *pg_owner;
+    int rc;
+
+    if ( (pg_owner = get_pg_owner(domid)) == NULL )
+        return -ESRCH;
+
+    rc = __do_update_va_mapping(va, ((uint64_t)hi << 32) | lo, flags, pg_owner);
+
+    put_pg_owner(pg_owner);
+
+    if ( rc == -EAGAIN )
+        rc = hypercall_create_continuation(
+            __HYPERVISOR_update_va_mapping_otherdomain,
+            "iiiii", va, lo, hi, flags, domid);
+
     return rc;
 }
 
--- a/xen/arch/x86/x86_64/compat/mm.c
+++ b/xen/arch/x86/x86_64/compat/mm.c
@@ -244,19 +244,6 @@ int compat_arch_memory_op(int op, XEN_GU
     return rc;
 }
 
-int compat_update_va_mapping(unsigned int va, u32 lo, u32 hi,
-                             unsigned int flags)
-{
-    return do_update_va_mapping(va, lo | ((u64)hi << 32), flags);
-}
-
-int compat_update_va_mapping_otherdomain(unsigned long va, u32 lo, u32 hi,
-                                         unsigned long flags,
-                                         domid_t domid)
-{
-    return do_update_va_mapping_otherdomain(va, lo | ((u64)hi << 32), flags, domid);
-}
-
 DEFINE_XEN_GUEST_HANDLE(mmuext_op_compat_t);
 
 int compat_mmuext_op(XEN_GUEST_HANDLE(mmuext_op_compat_t) cmp_uops,
