s390/vdso: add vdso randomization

Randomize the address of vdso if randomize_va_space is enabled.
Note that this keeps the vdso address on the same PMD as the stack
to avoid allocating an extra page table just for vdso.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index 7ba84a8..5075cde 100644 (file)
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 #include <linux/smp.h>
 #include <linux/time_namespace.h>
+#include <linux/random.h>
 #include <vdso/datapage.h>
 #include <asm/vdso.h>
 
@@ -208,6 +209,31 @@ out:
        return rc;
 }
 
+static unsigned long vdso_addr(unsigned long start, unsigned long len)
+{
+       unsigned long addr, end, offset;
+
+       /*
+        * Round up the start address. It can start out unaligned as a result
+        * of stack start randomization.
+        */
+       start = PAGE_ALIGN(start);
+
+       /* Round the lowest possible end address up to a PMD boundary. */
+       end = (start + len + PMD_SIZE - 1) & PMD_MASK;
+       if (end >= VDSO_BASE)
+               end = VDSO_BASE;
+       end -= len;
+
+       if (end > start) {
+               offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
+               addr = start + (offset << PAGE_SHIFT);
+       } else {
+               addr = start;
+       }
+       return addr;
+}
+
 unsigned long vdso_size(void)
 {
        unsigned long size = VVAR_NR_PAGES * PAGE_SIZE;
@@ -221,7 +247,12 @@ unsigned long vdso_size(void)
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
-       return map_vdso(VDSO_BASE, vdso_size());
+       unsigned long addr = VDSO_BASE;
+       unsigned long size = vdso_size();
+
+       if (current->flags & PF_RANDOMIZE)
+               addr = vdso_addr(current->mm->start_stack + PAGE_SIZE, size);
+       return map_vdso(addr, size);
 }
 
 static struct page ** __init vdso_setup_pages(void *start, void *end)