ARM: initial stack protector (-fstack-protector) support

This is the very basic stuff without the changing canary upon
task switch yet.  Just the Kconfig option and a constant canary
value initialized at boot time.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 1f254bd..f160b93 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1374,6 +1374,18 @@ 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 64ba313..ddf6da1 100644 (file)
--- 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/stackprotector.h b/arch/arm/include/asm/stackprotector.h
new file mode 100644 (file)
index 0000000..de00332
--- /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/process.c b/arch/arm/kernel/process.c
index 1c6eb7e..090ac94 100644 (file)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -37,6 +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",