ARM: make vectors page inaccessible from userspace

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>

3 files changed, 12 insertions, 1 deletions

diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
index 6363f3d1d505..4355f0ec44d6 100644
--- a/arch/arm/include/asm/page.h
+++ b/arch/arm/include/asm/page.h
@@ -142,7 +142,9 @@ extern void __cpu_copy_user_highpage(struct page *to, struct page *from,
 #define clear_page(page)        memset((void *)(page), 0, PAGE_SIZE)
 extern void copy_page(void *to, const void *from);
 
+#ifdef CONFIG_KUSER_HELPERS
 #define __HAVE_ARCH_GATE_AREA 1
+#endif
 
 #ifdef CONFIG_ARM_LPAE
 #include <asm/pgtable-3level-types.h>
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 566d0d71a1e7..1e6c33d01c05 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -426,6 +426,7 @@ 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
@@ -458,10 +459,14 @@ 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;
 }
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 9ea274d1af69..ca46f413d867 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1205,7 +1205,11 @@ static void __init devicemaps_init(struct machine_desc *mdesc)
         map.pfn = __phys_to_pfn(virt_to_phys(vectors));
         map.virtual = 0xffff0000;
         map.length = PAGE_SIZE;
+#ifdef CONFIG_KUSER_HELPERS
         map.type = MT_HIGH_VECTORS;
+#else
+        map.type = MT_LOW_VECTORS;
+#endif
         create_mapping(&map);
 
         if (!vectors_high()) {