Merge branch 'core-stackprotector-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull strong stackprotector support from Ingo Molnar:
 "This tree adds a CONFIG_CC_STACKPROTECTOR_STRONG=y, a new, stronger
  stack canary checking method supported by the newest GCC versions (4.9
  and later).

  Here's the 'intensity comparison' between the various protection
  modes:

      - defconfig
        11430641 kernel text size
        36110 function bodies

      - defconfig + CONFIG_CC_STACKPROTECTOR_REGULAR
        11468490 kernel text size (+0.33%)
        1015 of 36110 functions are stack-protected (2.81%)

      - defconfig + CONFIG_CC_STACKPROTECTOR_STRONG via this patch
        11692790 kernel text size (+2.24%)
        7401 of 36110 functions are stack-protected (20.5%)

  the strong model comes with non-trivial costs, which is why we
  preserved the 'regular' and 'none' models as well"

* 'core-stackprotector-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG
  stackprotector: Unify the HAVE_CC_STACKPROTECTOR logic between architectures

3 files changed, 15 insertions, 16 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c1f1a7eee953..9c909fc29272 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -30,6 +30,7 @@ config ARM
 	select HAVE_BPF_JIT
 	select HAVE_CONTEXT_TRACKING
 	select HAVE_C_RECORDMCOUNT
+	select HAVE_CC_STACKPROTECTOR
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_API_DEBUG
 	select HAVE_DMA_ATTRS
@@ -1856,18 +1857,6 @@ config SECCOMP
 	  and the task is only allowed to execute a few safe syscalls
 	  defined by each seccomp mode.
 
-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.
-
 config SWIOTLB
 	def_bool y
 
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index c99b1086d83d..55b4255ad6ed 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -40,10 +40,6 @@ 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/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
index 31bd43b82095..d4f891f56996 100644
--- a/arch/arm/boot/compressed/misc.c
+++ b/arch/arm/boot/compressed/misc.c
@@ -127,6 +127,18 @@ asmlinkage void __div0(void)
 	error("Attempting division by 0!");
 }
 
+unsigned long __stack_chk_guard;
+
+void __stack_chk_guard_setup(void)
+{
+	__stack_chk_guard = 0x000a0dff;
+}
+
+void __stack_chk_fail(void)
+{
+	error("stack-protector: Kernel stack is corrupted\n");
+}
+
 extern int do_decompress(u8 *input, int len, u8 *output, void (*error)(char *x));
 
 
@@ -137,6 +149,8 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,
 {
 	int ret;
 
+	__stack_chk_guard_setup();
+
 	output_data		= (unsigned char *)output_start;
 	free_mem_ptr		= free_mem_ptr_p;
 	free_mem_end_ptr	= free_mem_ptr_end_p;