[Xen-changelog] [xen stable-4.8] x86/mm: Plumbing to allow any PTE update to fail with -ERESTART

[patchbot@xxxxxxx]

commit 7849d13d456916138d1b79fe92b0f8ee2fd60429
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jul 23 08:11:40 2018 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Aug 14 17:27:27 2018 +0100

    x86/mm: Plumbing to allow any PTE update to fail with -ERESTART
    
    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit c612481d1c9232c6abf91b03ec655e92f808805f)
---
 xen/arch/x86/mm.c               | 80 +++++++++++++++++++++++++++++++----------
 xen/arch/x86/x86_64/compat/mm.c | 13 -------
 xen/include/asm-x86/hypercall.h |  2 +-
 3 files changed, 63 insertions(+), 32 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index f439fc4e74..52f0d6bde9 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -747,6 +747,8 @@ static int get_page_from_pagenr(unsigned long page_nr, 
struct domain *d)
     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,
@@ -761,9 +763,7 @@ static int get_page_and_type_from_pagenr(unsigned long 
page_nr,
          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) )
@@ -1610,8 +1610,7 @@ static int create_pae_xen_mappings(struct domain *d, 
l3_pgentry_t *pl3e)
     return 1;
 }
 
-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);
@@ -1623,8 +1622,7 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type,
 
     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 = -ERESTART;
@@ -1635,6 +1633,12 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type,
              (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 )
             continue;
 
+        if ( unlikely(rc == -ERESTART) )
+        {
+            page->nr_validated_ptes = i;
+            break;
+        }
+
         if ( rc < 0 )
         {
             MEM_LOG("Failure in alloc_l2_table: entry %d", i);
@@ -1859,7 +1863,7 @@ static void free_l1_table(struct page_info *page)
 }
 
 
-static int free_l2_table(struct page_info *page, int preemptible)
+static int free_l2_table(struct page_info *page)
 {
     struct domain *d = page_get_owner(page);
     unsigned long pfn = page_to_mfn(page);
@@ -1873,7 +1877,7 @@ static int free_l2_table(struct page_info *page, int 
preemptible)
     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 = -ERESTART;
@@ -2478,7 +2482,8 @@ static int alloc_page_type(struct page_info *page, 
unsigned long type,
         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);
@@ -2569,7 +2574,8 @@ int free_page_type(struct page_info *page, unsigned long 
type,
         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:
         ASSERT(preemptible);
@@ -3859,12 +3865,9 @@ long do_mmuext_op(
     }
 
     if ( rc == -ERESTART )
-    {
-        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_PARAM(void) null;
@@ -4155,12 +4158,9 @@ long do_mmu_update(
     }
 
     if ( rc == -ERESTART )
-    {
-        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_PARAM(void) null;
@@ -4869,7 +4869,13 @@ 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 == -ERESTART )
+        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,
@@ -4886,10 +4892,48 @@ long do_update_va_mapping_otherdomain(unsigned long va, 
u64 val64,
 
     put_pg_owner(pg_owner);
 
+    if ( rc == -ERESTART )
+        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 == -ERESTART )
+        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 == -ERESTART )
+        rc = hypercall_create_continuation(
+            __HYPERVISOR_update_va_mapping_otherdomain,
+            "iiiii", va, lo, hi, flags, domid);
+
+    return rc;
+}
 
 /*************************
  * Descriptor Tables
diff --git a/xen/arch/x86/x86_64/compat/mm.c b/xen/arch/x86/x86_64/compat/mm.c
index 58be8ad7f1..41a0921f7c 100644
--- a/xen/arch/x86/x86_64/compat/mm.c
+++ b/xen/arch/x86/x86_64/compat/mm.c
@@ -200,19 +200,6 @@ int compat_arch_memory_op(unsigned long cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
     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_PARAM(void) arg,
diff --git a/xen/include/asm-x86/hypercall.h b/xen/include/asm-x86/hypercall.h
index c59aa69b14..7c3f46e183 100644
--- a/xen/include/asm-x86/hypercall.h
+++ b/xen/include/asm-x86/hypercall.h
@@ -158,7 +158,7 @@ extern int compat_update_va_mapping(
     unsigned int va, u32 lo, u32 hi, unsigned int flags);
 
 extern int compat_update_va_mapping_otherdomain(
-    unsigned long va, u32 lo, u32 hi, unsigned long flags, domid_t domid);
+    unsigned int va, u32 lo, u32 hi, unsigned int flags, domid_t domid);
 
 DEFINE_XEN_GUEST_HANDLE(trap_info_compat_t);
 extern int compat_set_trap_table(XEN_GUEST_HANDLE(trap_info_compat_t) traps);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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