ARM: Separate out access error checking

Since we get notified separately about prefetch aborts, which may be
permission faults, we need to check for appropriate access permissions
when handling a fault.  This patch prepares us for doing this by
separating out the access error checking.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 22 insertions, 11 deletions

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index b8b3bb4423c..b7ce07d416c 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -194,18 +194,33 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 #define VM_FAULT_BADMAP         0x010000
 #define VM_FAULT_BADACCESS      0x020000
 
-static int
+/*
+ * Check that the permissions on the VMA allow for the fault which occurred.
+ * If we encountered a write fault, we must have write permission, otherwise
+ * we allow any permission.
+ */
+static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
+{
+        unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
+
+        if (fsr & FSR_WRITE)
+                mask = VM_WRITE;
+
+        return vma->vm_flags & mask ? false : true;
+}
+
+static int __kprobes
 __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
                 struct task_struct *tsk)
 {
         struct vm_area_struct *vma;
-        int fault, mask;
+        int fault;
 
         vma = find_vma(mm, addr);
         fault = VM_FAULT_BADMAP;
-        if (!vma)
+        if (unlikely(!vma))
                 goto out;
-        if (vma->vm_start > addr)
+        if (unlikely(vma->vm_start > addr))
                 goto check_stack;
 
         /*
@@ -213,14 +228,10 @@ __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
          * memory access, so we can handle it.
          */
 good_area:
-        if (fsr & FSR_WRITE)
-                mask = VM_WRITE;
-        else
-                mask = VM_READ|VM_EXEC|VM_WRITE;
-
-        fault = VM_FAULT_BADACCESS;
-        if (!(vma->vm_flags & mask))
+        if (access_error(fsr, vma)) {
+                fault = VM_FAULT_BADACCESS;
                 goto out;
+        }
 
         /*
          * If for any reason at all we couldn't handle the fault, make