8 files changed, 85 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c171f35b73af..2244de273d2c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1375,6 +1375,18 @@ config UACCESS_WITH_MEMCPY
           However, if the CPU data cache is using a write-allocate mode,
           this option is unlikely to provide any performance gain.
 
+config CC_STACKPROTECTOR
+        bool "Enable -fstack-protector buffer overflow detection (EXPERIMENTAL)"
+        help
+          This option turns on the -fstack-protector GCC feature. This
+          feature puts, at the beginning of functions, a canary value on
+          the stack just before the return address, and validates
+          the value just before actually returning.  Stack based buffer
+          overflows (that need to overwrite this return address) now also
+          overwrite the canary, which gets detected and the attack is then
+          neutralized via a kernel panic.
+          This feature requires gcc version 4.2 or above.
+
 endmenu
 
 menu "Boot options"
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 64ba313724d2..ddf6da158ad8 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -34,6 +34,10 @@ ifeq ($(CONFIG_FRAME_POINTER),y)
 KBUILD_CFLAGS   +=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
 endif
 
+ifeq ($(CONFIG_CC_STACKPROTECTOR),y)
+KBUILD_CFLAGS   +=-fstack-protector
+endif
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN),y)
 KBUILD_CPPFLAGS += -mbig-endian
 AS              += -EB
diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index 51662feb9f1d..0a96e8c1b82a 100644
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -121,4 +121,7 @@ int dump_task_regs(struct task_struct *t, elf_gregset_t *elfregs);
 extern void elf_set_personality(const struct elf32_hdr *);
 #define SET_PERSONALITY(ex)     elf_set_personality(&(ex))
 
+extern unsigned long arch_randomize_brk(struct mm_struct *mm);
+#define arch_randomize_brk arch_randomize_brk
+
 #endif
diff --git a/arch/arm/include/asm/stackprotector.h b/arch/arm/include/asm/stackprotector.h
new file mode 100644
index 000000000000..de003327be97
--- /dev/null
+++ b/arch/arm/include/asm/stackprotector.h
@@ -0,0 +1,38 @@
+/*
+ * GCC stack protector support.
+ *
+ * Stack protector works by putting predefined pattern at the start of
+ * the stack frame and verifying that it hasn't been overwritten when
+ * returning from the function.  The pattern is called stack canary
+ * and gcc expects it to be defined by a global variable called
+ * "__stack_chk_guard" on ARM.  This unfortunately means that on SMP
+ * we cannot have a different canary value per task.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1
+
+#include <linux/random.h>
+#include <linux/version.h>
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return,
+ * and it must always be inlined.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+        unsigned long canary;
+
+        /* Try to get a semi random initial value. */
+        get_random_bytes(&canary, sizeof(canary));
+        canary ^= LINUX_VERSION_CODE;
+
+        current->stack_canary = canary;
+        __stack_chk_guard = current->stack_canary;
+}
+
+#endif  /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 883511522fca..85f2a019f77b 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -40,6 +40,9 @@
 int main(void)
 {
   DEFINE(TSK_ACTIVE_MM,         offsetof(struct task_struct, active_mm));
+#ifdef CONFIG_CC_STACKPROTECTOR
+  DEFINE(TSK_STACK_CANARY,      offsetof(struct task_struct, stack_canary));
+#endif
   BLANK();
   DEFINE(TI_FLAGS,              offsetof(struct thread_info, flags));
   DEFINE(TI_PREEMPT,            offsetof(struct thread_info, preempt_count));
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7ee48e7f8f31..2d14081b26b1 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -745,6 +745,11 @@ ENTRY(__switch_to)
         mov     r4, #0xffff0fff
         str     r3, [r4, #-15]                  @ TLS val at 0xffff0ff0
 #endif
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+        ldr     r7, [r2, #TI_TASK]
+        ldr     r8, =__stack_chk_guard
+        ldr     r7, [r7, #TSK_STACK_CANARY]
+#endif
 #ifdef CONFIG_MMU
         mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
 #endif
@@ -753,6 +758,9 @@ ENTRY(__switch_to)
         ldr     r0, =thread_notify_head
         mov     r1, #THREAD_NOTIFY_SWITCH
         bl      atomic_notifier_call_chain
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+        str     r7, [r8]
+#endif
  THUMB( mov     ip, r4                     )
         mov     r0, r5
  ARM(   ldmia   r4, {r4 - sl, fp, sp, pc}  )    @ Load all regs saved previously
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index acf5e6fdb6dc..090ac9459da1 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -28,6 +28,7 @@
 #include <linux/tick.h>
 #include <linux/utsname.h>
 #include <linux/uaccess.h>
+#include <linux/random.h>
 
 #include <asm/leds.h>
 #include <asm/processor.h>
@@ -36,6 +37,12 @@
 #include <asm/stacktrace.h>
 #include <asm/mach/time.h>
 
+#ifdef CONFIG_CC_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
 static const char *processor_modes[] = {
   "USER_26", "FIQ_26" , "IRQ_26" , "SVC_26" , "UK4_26" , "UK5_26" , "UK6_26" , "UK7_26" ,
   "UK8_26" , "UK9_26" , "UK10_26", "UK11_26", "UK12_26", "UK13_26", "UK14_26", "UK15_26",
@@ -421,3 +428,9 @@ unsigned long get_wchan(struct task_struct *p)
         } while (count ++ < 16);
         return 0;
 }
+
+unsigned long arch_randomize_brk(struct mm_struct *mm)
+{
+        unsigned long range_end = mm->brk + 0x02000000;
+        return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
+}
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index f5abc51c5a07..4f5b39687df5 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -7,6 +7,7 @@
 #include <linux/shm.h>
 #include <linux/sched.h>
 #include <linux/io.h>
+#include <linux/random.h>
 #include <asm/cputype.h>
 #include <asm/system.h>
 
@@ -80,6 +81,9 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
                 start_addr = addr = TASK_UNMAPPED_BASE;
                 mm->cached_hole_size = 0;
         }
+        /* 8 bits of randomness in 20 address space bits */
+        if (current->flags & PF_RANDOMIZE)
+                addr += (get_random_int() % (1 << 8)) << PAGE_SHIFT;
 
 full_search:
         if (do_align)