MIPS: Randomize mmap if randomize_va_space is set

Fairly straight forward: For 32-bit address spaces randomize within a
16MB space, for 64-bit within a 256MB space.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1480/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/arch/mips/kernel/syscall.c b/arch/mips/kernel/syscall.c
index dd81b0f87518..9824a829f61d 100644
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -29,6 +29,7 @@
 #include <linux/ipc.h>
 #include <linux/uaccess.h>
 #include <linux/slab.h>
+#include <linux/random.h>
 
 #include <asm/asm.h>
 #include <asm/branch.h>
@@ -116,7 +117,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
                     (!vmm || addr + len <= vmm->vm_start))
                         return addr;
         }
-        addr = TASK_UNMAPPED_BASE;
+        addr = current->mm->mmap_base;
         if (do_color_align)
                 addr = COLOUR_ALIGN(addr, pgoff);
         else
@@ -134,6 +135,24 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
         }
 }
 
+void arch_pick_mmap_layout(struct mm_struct *mm)
+{
+        unsigned long random_factor = 0UL;
+
+        if (current->flags & PF_RANDOMIZE) {
+                random_factor = get_random_int();
+                random_factor = random_factor << PAGE_SHIFT;
+                if (TASK_IS_32BIT_ADDR)
+                        random_factor &= 0xfffffful;
+                else
+                        random_factor &= 0xffffffful;
+        }
+
+        mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
+        mm->get_unmapped_area = arch_get_unmapped_area;
+        mm->unmap_area = arch_unmap_area;
+}
+
 SYSCALL_DEFINE6(mips_mmap, unsigned long, addr, unsigned long, len,
         unsigned long, prot, unsigned long, flags, unsigned long,
         fd, off_t, offset)