ARM: make vectors page inaccessible from userspace

commit a5463cd3435475386cbbe7b06e01292ac169d36f upstream.

If kuser helpers are not provided by the kernel, disable user access to
the vectors page.  With the kuser helpers gone, there is no reason for
this page to be visible to userspace.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 72315e7be22b..1ed29cc22979 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -433,6 +433,7 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 }
 
 #ifdef CONFIG_MMU
+#ifdef CONFIG_KUSER_HELPERS
 /*
  * The vectors page is always readable from user space for the
  * atomic helpers. Insert it into the gate_vma so that it is visible
@@ -465,10 +466,14 @@ int in_gate_area_no_mm(unsigned long addr)
 {
         return in_gate_area(NULL, addr);
 }
+#define is_gate_vma(vma)        ((vma) = &gate_vma)
+#else
+#define is_gate_vma(vma)        0
+#endif
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
-        return (vma == &gate_vma) ? "[vectors]" :
+        return is_gate_vma(vma) ? "[vectors]" :
                 (vma->vm_mm && vma->vm_start == vma->vm_mm->context.sigpage) ?
                  "[sigpage]" : NULL;
 }