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>

arch/mips/include/asm/processor.h

@@ -33,6 +33,11 @@ extern void (*cpu_wait)(void);
 
 extern unsigned int vced_count, vcei_count;
 
+/*
+ * MIPS does have an arch_pick_mmap_layout()
+ */
+#define HAVE_ARCH_PICK_MMAP_LAYOUT 1
+
 /*
  * A special page (the vdso) is mapped into all processes at the very
  * top of the virtual memory space.
@@ -52,6 +57,9 @@ extern unsigned int vced_count, vcei_count;
  * space during mmap's.
  */
 #define TASK_UNMAPPED_BASE	((TASK_SIZE / 3) & ~(PAGE_SIZE))
+
+#define TASK_IS_32BIT_ADDR 1
+
 #endif
 
 #ifdef CONFIG_64BIT
@@ -77,6 +85,9 @@ extern unsigned int vced_count, vcei_count;
 		PAGE_ALIGN(TASK_SIZE32 / 3) : PAGE_ALIGN(TASK_SIZE / 3))
 #define TASK_SIZE_OF(tsk)						\
 	(test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE)
+
+#define TASK_IS_32BIT_ADDR test_thread_flag(TIF_32BIT_ADDR)
+
 #endif
 
 #ifdef __KERNEL__

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)