s390/mm: downgrade page table after fork of a 31 bit process

The downgrade of the 4 level page table created by init_new_context is
currently done only in start_thread31. If a 31 bit process forks the
new mm uses a 4 level page table, including the task size of 2<<42
that goes along with it. This is incorrect as now a 31 bit process
can map memory beyond 2GB. Define arch_dup_mmap to do the downgrade
after fork.

Cc: stable@vger.kernel.org
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

4 files changed, 25 insertions, 8 deletions

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 5c63615f1349..077de7efc82f 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -11,7 +11,6 @@
 #include <asm/uaccess.h>
 #include <asm/tlbflush.h>
 #include <asm/ctl_reg.h>
-#include <asm-generic/mm_hooks.h>
 
 static inline int init_new_context(struct task_struct *tsk,
                                    struct mm_struct *mm)
@@ -91,4 +90,17 @@ static inline void activate_mm(struct mm_struct *prev,
         switch_mm(prev, next, current);
 }
 
+static inline void arch_dup_mmap(struct mm_struct *oldmm,
+                                 struct mm_struct *mm)
+{
+#ifdef CONFIG_64BIT
+        if (oldmm->context.asce_limit < mm->context.asce_limit)
+                crst_table_downgrade(mm, oldmm->context.asce_limit);
+#endif
+}
+
+static inline void arch_exit_mmap(struct mm_struct *mm)
+{
+}
+
 #endif /* __S390_MMU_CONTEXT_H */
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index c40fa91e38a8..11e4e3236937 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -120,7 +120,9 @@ struct stack_frame {
         regs->psw.mask  = psw_user_bits | PSW_MASK_BA;                  \
         regs->psw.addr  = new_psw | PSW_ADDR_AMODE;                     \
         regs->gprs[15]  = new_stackp;                                   \
+        __tlb_flush_mm(current->mm);                                    \
         crst_table_downgrade(current->mm, 1UL << 31);                   \
+        update_mm(current->mm, current);                                \
 } while (0)
 
 /* Forward declaration, a strange C thing */
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 573384256c5c..c59a5efa58b1 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -103,9 +103,15 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 
 int s390_mmap_check(unsigned long addr, unsigned long len)
 {
+        int rc;
+
         if (!is_compat_task() &&
-            len >= TASK_SIZE && TASK_SIZE < (1UL << 53))
-                return crst_table_upgrade(current->mm, 1UL << 53);
+            len >= TASK_SIZE && TASK_SIZE < (1UL << 53)) {
+                rc = crst_table_upgrade(current->mm, 1UL << 53);
+                if (rc)
+                        return rc;
+                update_mm(current->mm, current);
+        }
         return 0;
 }
 
@@ -125,6 +131,7 @@ s390_get_unmapped_area(struct file *filp, unsigned long addr,
                 rc = crst_table_upgrade(mm, 1UL << 53);
                 if (rc)
                         return (unsigned long) rc;
+                update_mm(mm, current);
                 area = arch_get_unmapped_area(filp, addr, len, pgoff, flags);
         }
         return area;
@@ -147,6 +154,7 @@ s390_get_unmapped_area_topdown(struct file *filp, const unsigned long addr,
                 rc = crst_table_upgrade(mm, 1UL << 53);
                 if (rc)
                         return (unsigned long) rc;
+                update_mm(mm, current);
                 area = arch_get_unmapped_area_topdown(filp, addr, len,
                                                       pgoff, flags);
         }
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 1cab221077cc..e9ac2d60b7e5 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -85,7 +85,6 @@ repeat:
                 crst_table_free(mm, table);
         if (mm->context.asce_limit < limit)
                 goto repeat;
-        update_mm(mm, current);
         return 0;
 }
 
@@ -93,9 +92,6 @@ void crst_table_downgrade(struct mm_struct *mm, unsigned long limit)
 {
         pgd_t *pgd;
 
-        if (mm->context.asce_limit <= limit)
-                return;
-        __tlb_flush_mm(mm);
         while (mm->context.asce_limit > limit) {
                 pgd = mm->pgd;
                 switch (pgd_val(*pgd) & _REGION_ENTRY_TYPE_MASK) {
@@ -118,7 +114,6 @@ void crst_table_downgrade(struct mm_struct *mm, unsigned long limit)
                 mm->task_size = mm->context.asce_limit;
                 crst_table_free(mm, (unsigned long *) pgd);
         }
-        update_mm(mm, current);
 }
 #endif