[Xen-devel] [PATCH 1/2] x86: cleanup after making various page table manipulation operations preemptible

["Jan Beulich" <JBeulich@xxxxxxxx>]

This drops the "preemptible" parameters from various functions where
now they can't (or shouldn't, validated by assertions) be run in non-
preemptible mode anymore, to prove that manipulations of at least L3
and L4 page tables and page table entries are now always preemptible,
i.e. the earlier patches actually fulfill their purpose of fixing the
resulting security issue.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Tim Deegan <tim@xxxxxxx>

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1859,7 +1859,7 @@ static int relinquish_memory(
         }
 
         if ( test_and_clear_bit(_PGT_pinned, &page->u.inuse.type_info) )
-            ret = put_page_and_type_preemptible(page, 1);
+            ret = put_page_and_type_preemptible(page);
         switch ( ret )
         {
         case 0:
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -943,7 +943,7 @@ get_page_from_l2e(
 define_get_linear_pagetable(l3);
 static int
 get_page_from_l3e(
-    l3_pgentry_t l3e, unsigned long pfn, struct domain *d, int partial, int 
preemptible)
+    l3_pgentry_t l3e, unsigned long pfn, struct domain *d, int partial)
 {
     int rc;
 
@@ -957,7 +957,7 @@ get_page_from_l3e(
     }
 
     rc = get_page_and_type_from_pagenr(
-        l3e_get_pfn(l3e), PGT_l2_page_table, d, partial, preemptible);
+        l3e_get_pfn(l3e), PGT_l2_page_table, d, partial, 1);
     if ( unlikely(rc == -EINVAL) && get_l3_linear_pagetable(l3e, pfn, d) )
         rc = 0;
 
@@ -967,7 +967,7 @@ get_page_from_l3e(
 define_get_linear_pagetable(l4);
 static int
 get_page_from_l4e(
-    l4_pgentry_t l4e, unsigned long pfn, struct domain *d, int partial, int 
preemptible)
+    l4_pgentry_t l4e, unsigned long pfn, struct domain *d, int partial)
 {
     int rc;
 
@@ -981,7 +981,7 @@ get_page_from_l4e(
     }
 
     rc = get_page_and_type_from_pagenr(
-        l4e_get_pfn(l4e), PGT_l3_page_table, d, partial, preemptible);
+        l4e_get_pfn(l4e), PGT_l3_page_table, d, partial, 1);
     if ( unlikely(rc == -EINVAL) && get_l4_linear_pagetable(l4e, pfn, d) )
         rc = 0;
 
@@ -1120,8 +1120,10 @@ static int put_page_from_l2e(l2_pgentry_
 static int __put_page_type(struct page_info *, int preemptible);
 
 static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn,
-                             int partial, int preemptible)
+                             int partial, bool_t defer)
 {
+    struct page_info *pg;
+
     if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) || (l3e_get_pfn(l3e) == pfn) )
         return 1;
 
@@ -1138,40 +1140,44 @@ static int put_page_from_l3e(l3_pgentry_
         return 0;
     }
 
+    pg = l3e_get_page(l3e);
+
     if ( unlikely(partial > 0) )
     {
-        ASSERT(preemptible >= 0);
-        return __put_page_type(l3e_get_page(l3e), preemptible);
+        ASSERT(!defer);
+        return __put_page_type(pg, 1);
     }
 
-    if ( preemptible < 0 )
+    if ( defer )
     {
-        current->arch.old_guest_table = l3e_get_page(l3e);
+        current->arch.old_guest_table = pg;
         return 0;
     }
 
-    return put_page_and_type_preemptible(l3e_get_page(l3e), preemptible);
+    return put_page_and_type_preemptible(pg);
 }
 
 static int put_page_from_l4e(l4_pgentry_t l4e, unsigned long pfn,
-                             int partial, int preemptible)
+                             int partial, bool_t defer)
 {
     if ( (l4e_get_flags(l4e) & _PAGE_PRESENT) && 
          (l4e_get_pfn(l4e) != pfn) )
     {
+        struct page_info *pg = l4e_get_page(l4e);
+
         if ( unlikely(partial > 0) )
         {
-            ASSERT(preemptible >= 0);
-            return __put_page_type(l4e_get_page(l4e), preemptible);
+            ASSERT(!defer);
+            return __put_page_type(pg, 1);
         }
 
-        if ( preemptible < 0 )
+        if ( defer )
         {
-            current->arch.old_guest_table = l4e_get_page(l4e);
+            current->arch.old_guest_table = pg;
             return 0;
         }
 
-        return put_page_and_type_preemptible(l4e_get_page(l4e), preemptible);
+        return put_page_and_type_preemptible(pg);
     }
     return 1;
 }
@@ -1305,7 +1311,7 @@ static int alloc_l2_table(struct page_in
     return rc > 0 ? 0 : rc;
 }
 
-static int alloc_l3_table(struct page_info *page, int preemptible)
+static int alloc_l3_table(struct page_info *page)
 {
     struct domain *d = page_get_owner(page);
     unsigned long  pfn = page_to_mfn(page);
@@ -1337,11 +1343,10 @@ static int alloc_l3_table(struct page_in
                 rc = get_page_and_type_from_pagenr(l3e_get_pfn(pl3e[i]),
                                                    PGT_l2_page_table |
                                                    PGT_pae_xen_l2,
-                                                   d, partial, preemptible);
+                                                   d, partial, 1);
         }
         else if ( !is_guest_l3_slot(i) ||
-                  (rc = get_page_from_l3e(pl3e[i], pfn, d,
-                                          partial, preemptible)) > 0 )
+                  (rc = get_page_from_l3e(pl3e[i], pfn, d, partial)) > 0 )
             continue;
 
         if ( rc == -EAGAIN )
@@ -1401,7 +1406,7 @@ void init_guest_l4_table(l4_pgentry_t l4
         l4e_from_page(d->arch.perdomain_l3_pg, __PAGE_HYPERVISOR);
 }
 
-static int alloc_l4_table(struct page_info *page, int preemptible)
+static int alloc_l4_table(struct page_info *page)
 {
     struct domain *d = page_get_owner(page);
     unsigned long  pfn = page_to_mfn(page);
@@ -1413,8 +1418,7 @@ static int alloc_l4_table(struct page_in
           i++, partial = 0 )
     {
         if ( !is_guest_l4_slot(d, i) ||
-             (rc = get_page_from_l4e(pl4e[i], pfn, d,
-                                     partial, preemptible)) > 0 )
+             (rc = get_page_from_l4e(pl4e[i], pfn, d, partial)) > 0 )
             continue;
 
         if ( rc == -EAGAIN )
@@ -1501,7 +1505,7 @@ static int free_l2_table(struct page_inf
     return err;
 }
 
-static int free_l3_table(struct page_info *page, int preemptible)
+static int free_l3_table(struct page_info *page)
 {
     struct domain *d = page_get_owner(page);
     unsigned long pfn = page_to_mfn(page);
@@ -1514,7 +1518,7 @@ static int free_l3_table(struct page_inf
     do {
         if ( is_guest_l3_slot(i) )
         {
-            rc = put_page_from_l3e(pl3e[i], pfn, partial, preemptible);
+            rc = put_page_from_l3e(pl3e[i], pfn, partial, 0);
             if ( rc < 0 )
                 break;
             partial = 0;
@@ -1540,7 +1544,7 @@ static int free_l3_table(struct page_inf
     return rc > 0 ? 0 : rc;
 }
 
-static int free_l4_table(struct page_info *page, int preemptible)
+static int free_l4_table(struct page_info *page)
 {
     struct domain *d = page_get_owner(page);
     unsigned long pfn = page_to_mfn(page);
@@ -1550,7 +1554,7 @@ static int free_l4_table(struct page_inf
 
     do {
         if ( is_guest_l4_slot(d, i) )
-            rc = put_page_from_l4e(pl4e[i], pfn, partial, preemptible);
+            rc = put_page_from_l4e(pl4e[i], pfn, partial, 0);
         if ( rc < 0 )
             break;
         partial = 0;
@@ -1809,7 +1813,6 @@ static int mod_l3_entry(l3_pgentry_t *pl
                         l3_pgentry_t nl3e, 
                         unsigned long pfn,
                         int preserve_ad,
-                        int preemptible,
                         struct vcpu *vcpu)
 {
     l3_pgentry_t ol3e;
@@ -1849,7 +1852,7 @@ static int mod_l3_entry(l3_pgentry_t *pl
             return rc ? 0 : -EFAULT;
         }
 
-        rc = get_page_from_l3e(nl3e, pfn, d, 0, preemptible);
+        rc = get_page_from_l3e(nl3e, pfn, d, 0);
         if ( unlikely(rc < 0) )
             return rc;
         rc = 0;
@@ -1872,7 +1875,7 @@ static int mod_l3_entry(l3_pgentry_t *pl
         if ( !create_pae_xen_mappings(d, pl3e) )
             BUG();
 
-    put_page_from_l3e(ol3e, pfn, 0, -preemptible);
+    put_page_from_l3e(ol3e, pfn, 0, 1);
     return rc;
 }
 
@@ -1881,7 +1884,6 @@ static int mod_l4_entry(l4_pgentry_t *pl
                         l4_pgentry_t nl4e, 
                         unsigned long pfn,
                         int preserve_ad,
-                        int preemptible,
                         struct vcpu *vcpu)
 {
     struct domain *d = vcpu->domain;
@@ -1914,7 +1916,7 @@ static int mod_l4_entry(l4_pgentry_t *pl
             return rc ? 0 : -EFAULT;
         }
 
-        rc = get_page_from_l4e(nl4e, pfn, d, 0, preemptible);
+        rc = get_page_from_l4e(nl4e, pfn, d, 0);
         if ( unlikely(rc < 0) )
             return rc;
         rc = 0;
@@ -1933,7 +1935,7 @@ static int mod_l4_entry(l4_pgentry_t *pl
         return -EFAULT;
     }
 
-    put_page_from_l4e(ol4e, pfn, 0, -preemptible);
+    put_page_from_l4e(ol4e, pfn, 0, 1);
     return rc;
 }
 
@@ -2053,10 +2055,12 @@ static int alloc_page_type(struct page_i
         rc = alloc_l2_table(page, type, preemptible);
         break;
     case PGT_l3_page_table:
-        rc = alloc_l3_table(page, preemptible);
+        ASSERT(preemptible);
+        rc = alloc_l3_table(page);
         break;
     case PGT_l4_page_table:
-        rc = alloc_l4_table(page, preemptible);
+        ASSERT(preemptible);
+        rc = alloc_l4_table(page);
         break;
     case PGT_seg_desc_page:
         rc = alloc_segdesc_page(page);
@@ -2146,10 +2150,12 @@ int free_page_type(struct page_info *pag
         rc = free_l2_table(page, preemptible);
         break;
     case PGT_l3_page_table:
-        rc = free_l3_table(page, preemptible);
+        ASSERT(preemptible);
+        rc = free_l3_table(page);
         break;
     case PGT_l4_page_table:
-        rc = free_l4_table(page, preemptible);
+        ASSERT(preemptible);
+        rc = free_l4_table(page);
         break;
     default:
         MEM_LOG("type %lx pfn %lx\n", type, page_to_mfn(page));
@@ -2620,7 +2626,7 @@ static int put_old_guest_table(struct vc
     if ( !v->arch.old_guest_table )
         return 0;
 
-    switch ( rc = put_page_and_type_preemptible(v->arch.old_guest_table, 1) )
+    switch ( rc = put_page_and_type_preemptible(v->arch.old_guest_table) )
     {
     case -EINTR:
     case -EAGAIN:
@@ -2654,7 +2660,7 @@ int vcpu_destroy_pagetables(struct vcpu 
         if ( paging_mode_refcounts(v->domain) )
             put_page(page);
         else
-            rc = put_page_and_type_preemptible(page, 1);
+            rc = put_page_and_type_preemptible(page);
     }
 
     if ( l4tab )
@@ -2675,7 +2681,7 @@ int vcpu_destroy_pagetables(struct vcpu 
             if ( paging_mode_refcounts(v->domain) )
                 put_page(page);
             else
-                rc = put_page_and_type_preemptible(page, 1);
+                rc = put_page_and_type_preemptible(page);
         }
         if ( !rc )
             v->arch.guest_table_user = pagetable_null();
@@ -2705,7 +2711,7 @@ int new_guest_cr3(unsigned long mfn)
                     l4e_from_pfn(
                         mfn,
                         (_PAGE_PRESENT|_PAGE_RW|_PAGE_USER|_PAGE_ACCESSED)),
-                    gt_mfn, 0, 1, curr);
+                    gt_mfn, 0, curr);
         unmap_domain_page(pl4e);
         switch ( rc )
         {
@@ -2769,7 +2775,7 @@ int new_guest_cr3(unsigned long mfn)
         if ( paging_mode_refcounts(d) )
             put_page(page);
         else
-            switch ( rc = put_page_and_type_preemptible(page, 1) )
+            switch ( rc = put_page_and_type_preemptible(page) )
             {
             case -EINTR:
                 rc = -EAGAIN;
@@ -3053,7 +3059,7 @@ long do_mmuext_op(
                 break;
             }
 
-            switch ( rc = put_page_and_type_preemptible(page, 1) )
+            switch ( rc = put_page_and_type_preemptible(page) )
             {
             case -EINTR:
             case -EAGAIN:
@@ -3129,7 +3135,7 @@ long do_mmuext_op(
                 if ( paging_mode_refcounts(d) )
                     put_page(page);
                 else
-                    switch ( rc = put_page_and_type_preemptible(page, 1) )
+                    switch ( rc = put_page_and_type_preemptible(page) )
                     {
                     case -EINTR:
                         rc = -EAGAIN;
@@ -3604,11 +3610,11 @@ long do_mmu_update(
                     break;
                 case PGT_l3_page_table:
                     rc = mod_l3_entry(va, l3e_from_intpte(req.val), mfn,
-                                      cmd == MMU_PT_UPDATE_PRESERVE_AD, 1, v);
+                                      cmd == MMU_PT_UPDATE_PRESERVE_AD, v);
                     break;
                 case PGT_l4_page_table:
                     rc = mod_l4_entry(va, l4e_from_intpte(req.val), mfn,
-                                      cmd == MMU_PT_UPDATE_PRESERVE_AD, 1, v);
+                                      cmd == MMU_PT_UPDATE_PRESERVE_AD, v);
                 break;
                 case PGT_writable_page:
                     perfc_incr(writable_mmu_updates);
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -364,15 +364,10 @@ static inline void put_page_and_type(str
     put_page(page);
 }
 
-static inline int put_page_and_type_preemptible(struct page_info *page,
-                                                int preemptible)
+static inline int put_page_and_type_preemptible(struct page_info *page)
 {
-    int rc = 0;
+    int rc = put_page_type_preemptible(page);
 
-    if ( preemptible )
-        rc = put_page_type_preemptible(page);
-    else
-        put_page_type(page);
     if ( likely(rc == 0) )
         put_page(page);
     return rc;

Attachment: x86-preemptible-cleanup.patch
Description: Text document

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel