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Commit c743f380 authored by Nicolas Pitre's avatar Nicolas Pitre
Browse files

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: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
parent cc92c28b

arch/arm/Kconfig

+12 −0
Original line number Diff line number Diff line
@@ -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"

arch/arm/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -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

arch/arm/include/asm/stackprotector.h

0 → 100644
+38 −0
Original line number Diff line number Diff line 
/*

 * 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 */

arch/arm/kernel/process.c

+6 −0
Original line number Diff line number Diff line
@@ -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",