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[PATCH 3.13.y-ckt 03/78] stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG

From Kamal Mostafa <kamal@canonical.com>
Newsgroups linux.kernel
Subject [PATCH 3.13.y-ckt 03/78] stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG
Date 2015-12-17 02:00 +0100
Message-ID <qGv5h-DM-45@gated-at.bofh.it> (permalink)
References <qGuVA-Ae-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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3.13.11-ckt32 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

commit 8779657d29c0ebcc0c94ede4df2f497baf1b563f upstream.

This changes the stack protector config option into a choice of
"None", "Regular", and "Strong":

   CONFIG_CC_STACKPROTECTOR_NONE
   CONFIG_CC_STACKPROTECTOR_REGULAR
   CONFIG_CC_STACKPROTECTOR_STRONG

"Regular" means the old CONFIG_CC_STACKPROTECTOR=y option.

"Strong" is a new mode introduced by this patch. With "Strong" the
kernel is built with -fstack-protector-strong (available in
gcc 4.9 and later). This option increases the coverage of the stack
protector without the heavy performance hit of -fstack-protector-all.

For reference, the stack protector options available in gcc are:

-fstack-protector-all:
  Adds the stack-canary saving prefix and stack-canary checking
  suffix to _all_ function entry and exit. Results in substantial
  use of stack space for saving the canary for deep stack users
  (e.g. historically xfs), and measurable (though shockingly still
  low) performance hit due to all the saving/checking. Really not
  suitable for sane systems, and was entirely removed as an option
  from the kernel many years ago.

-fstack-protector:
  Adds the canary save/check to functions that define an 8
  (--param=ssp-buffer-size=N, N=8 by default) or more byte local
  char array. Traditionally, stack overflows happened with
  string-based manipulations, so this was a way to find those
  functions. Very few total functions actually get the canary; no
  measurable performance or size overhead.

-fstack-protector-strong
  Adds the canary for a wider set of functions, since it's not
  just those with strings that have ultimately been vulnerable to
  stack-busting. With this superset, more functions end up with a
  canary, but it still remains small compared to all functions
  with only a small change in performance. Based on the original
  design document, a function gets the canary when it contains any
  of:

    - local variable's address used as part of the right hand side
      of an assignment or function argument
    - local variable is an array (or union containing an array),
      regardless of array type or length
    - uses register local variables

  https://docs.google.com/a/google.com/document/d/1xXBH6rRZue4f296vGt9YQcuLVQHeE516stHwt8M9xyU

Find below a comparison of "size" and "objdump" output when built with
gcc-4.9 in three configurations:

  - 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%)

With -strong, ARM's compressed boot code now triggers stack
protection, so a static guard was added. Since this is only used
during decompression and was never used before, the exposure
here is very small. Once it switches to the full kernel, the
stack guard is back to normal.

Chrome OS has been using -fstack-protector-strong for its kernel
builds for the last 8 months with no problems.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@linux-mips.org
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/1387481759-14535-3-git-send-email-keescook@chromium.org
[ Improved the changelog and descriptions some more. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[ kamal: 3.13-stable: need these arch/arm/boot/compressed/misc.c __stack_chk
  canary functions, even for just the old CONFIG_CC_STACKPROTECTOR ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 Makefile                        |  8 ++++++-
 arch/Kconfig                    | 51 ++++++++++++++++++++++++++++++++++++++---
 arch/arm/boot/compressed/misc.c | 14 +++++++++++
 3 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 58a799e..b43786f 100644
--- a/Makefile
+++ b/Makefile
@@ -598,12 +598,18 @@ KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
 endif
 
 # Handle stack protector mode.
-ifdef CONFIG_CC_STACKPROTECTOR
+ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
   stackp-flag := -fstack-protector
   ifeq ($(call cc-option, $(stackp-flag)),)
     $(warning Cannot use CONFIG_CC_STACKPROTECTOR: \
 	      -fstack-protector not supported by compiler))
   endif
+else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
+  stackp-flag := -fstack-protector-strong
+  ifeq ($(call cc-option, $(stackp-flag)),)
+    $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
+	      -fstack-protector-strong not supported by compiler)
+  endif
 else
   # Force off for distro compilers that enable stack protector by default.
   stackp-flag := $(call cc-option, -fno-stack-protector)
diff --git a/arch/Kconfig b/arch/Kconfig
index 24e026d..80bbb8c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -344,10 +344,17 @@ config HAVE_CC_STACKPROTECTOR
 	  - it has implemented a stack canary (e.g. __stack_chk_guard)
 
 config CC_STACKPROTECTOR
-	bool "Enable -fstack-protector buffer overflow detection"
+	def_bool n
+	help
+	  Set when a stack-protector mode is enabled, so that the build
+	  can enable kernel-side support for the GCC feature.
+
+choice
+	prompt "Stack Protector buffer overflow detection"
 	depends on HAVE_CC_STACKPROTECTOR
+	default CC_STACKPROTECTOR_NONE
 	help
-	  This option turns on the -fstack-protector GCC feature. This
+	  This option turns on the "stack-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
@@ -355,8 +362,46 @@ config CC_STACKPROTECTOR
 	  overwrite the canary, which gets detected and the attack is then
 	  neutralized via a kernel panic.
 
+config CC_STACKPROTECTOR_NONE
+	bool "None"
+	help
+	  Disable "stack-protector" GCC feature.
+
+config CC_STACKPROTECTOR_REGULAR
+	bool "Regular"
+	select CC_STACKPROTECTOR
+	help
+	  Functions will have the stack-protector canary logic added if they
+	  have an 8-byte or larger character array on the stack.
+
 	  This feature requires gcc version 4.2 or above, or a distribution
-	  gcc with the feature backported.
+	  gcc with the feature backported ("-fstack-protector").
+
+	  On an x86 "defconfig" build, this feature adds canary checks to
+	  about 3% of all kernel functions, which increases kernel code size
+	  by about 0.3%.
+
+config CC_STACKPROTECTOR_STRONG
+	bool "Strong"
+	select CC_STACKPROTECTOR
+	help
+	  Functions will have the stack-protector canary logic added in any
+	  of the following conditions:
+
+	  - local variable's address used as part of the right hand side of an
+	    assignment or function argument
+	  - local variable is an array (or union containing an array),
+	    regardless of array type or length
+	  - uses register local variables
+
+	  This feature requires gcc version 4.9 or above, or a distribution
+	  gcc with the feature backported ("-fstack-protector-strong").
+
+	  On an x86 "defconfig" build, this feature adds canary checks to
+	  about 20% of all kernel functions, which increases the kernel code
+	  size by about 2%.
+
+endchoice
 
 config HAVE_CONTEXT_TRACKING
 	bool
diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
index 31bd43b..d4f891f 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;
-- 
1.9.1

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[3.13.y-ckt stable] Linux 3.13.11-ckt32 stable review Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 38/78] vfs: Make sendfile(2) killable even better Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 56/78] sched/core: Clear the root_domain cpumasks in init_rootdomain() Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
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  [PATCH 3.13.y-ckt 62/78] tcp: md5: fix lockdep annotation Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 63/78] ARM: dts: Kirkwood: Fix QNAP TS219 power-off Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 47/78] drm/radeon: make some dpm errors debug only Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 04/78] iio: lpc32xx_adc: fix warnings caused by enabling unprepared clock Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 27/78] USB: option: add XS Stick W100-2 from 4G Systems Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
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  [PATCH 3.13.y-ckt 75/78] net: ip6mr: fix static mfc/dev leaks on table destruction Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
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  [PATCH 3.13.y-ckt 65/78] remoteproc: avoid stack overflow in debugfs file Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
  [PATCH 3.13.y-ckt 76/78] unix: avoid use-after-free in ep_remove_wait_queue Kamal Mostafa <kamal@canonical.com> - 2015-12-17 01:50 +0100
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  [PATCH 3.13.y-ckt 58/78] mmc: remove bondage between REQ_META and reliable write Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 55/78] wan/x25: Fix use-after-free in x25_asy_open_tty() Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
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  [PATCH 3.13.y-ckt 46/78] btrfs: fix signed overflows in btrfs_sync_file Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 37/78] fix sysvfs symlinks Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 51/78] target: Fix race for SCF_COMPARE_AND_WRITE_POST checking Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 48/78] nfs: if we have no valid attrs, then don't declare the attribute cache valid Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
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  [PATCH 3.13.y-ckt 54/78] Fix a memory leak in scsi_host_dev_release() Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 57/78] x86/signal: Fix restart_syscall number for x32 tasks Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 43/78] arm64: KVM: Fix AArch32 to AArch64 register mapping Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 50/78] iscsi-target: Fix rx_login_comp hang after login failure Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
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  [PATCH 3.13.y-ckt 53/78] block: Always check queue limits for cloned requests Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 03/78] stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 59/78] sctp: translate host order to network order when setting a hmacid Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 52/78] target: fix COMPARE_AND_WRITE non zero SGL offset data corruption Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:00 +0100
  [PATCH 3.13.y-ckt 36/78] ARC: dw2 unwind: Remove falllback linear search thru FDE entries Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 31/78] fat: fix fake_offset handling on error path Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 42/78] ring-buffer: Update read stamp with first real commit on page Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 15/78] mac80211: mesh: fix call_rcu() usage Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 44/78] drm/radeon: make rv770_set_sw_state failures non-fatal Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
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  [PATCH 3.13.y-ckt 33/78] parisc: Drop unused MADV_xxxK_PAGES flags from asm/mman.h Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 19/78] MIPS: KVM: Fix ASID restoration logic Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 23/78] xhci: Fix a race in usb2 LPM resume, blocking U3 for usb2 devices Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 32/78] kernel/signal.c: unexport sigsuspend() Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 21/78] MIPS: KVM: Uninit VCPU in vcpu_create error path Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 12/78] USB: serial: option: add support for Novatel MiFi USB620L Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 22/78] xhci: Workaround to get Intel xHCI reset working more reliably Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 16/78] usb: dwc3: gadget: let us set lower max_speed Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 40/78] nfs4: start callback_ident at idr 1 Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 14/78] ASoC: wm8962: correct addresses for HPF_C_0/1 Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
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  [PATCH 3.13.y-ckt 28/78] usblp: do not set TASK_INTERRUPTIBLE before lock Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 20/78] MIPS: KVM: Fix CACHE immediate offset sign extension Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 39/78] vfs: Avoid softlockups with sendfile(2) Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 25/78] ALSA: hda - Add fixup for Acer Aspire One Cloudbook 14 Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 29/78] mac: validate mac_partition is within sector Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 24/78] x86/cpu: Fix SMAP check in PVOPS environments Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 26/78] arm64: restore bogomips information in /proc/cpuinfo Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:10 +0100
  [PATCH 3.13.y-ckt 05/78] iio:ad5064: Make sure ad5064_i2c_write() returns 0 on success Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 10/78] ALSA: usb-audio: prevent CH345 multiport output SysEx corruption Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 11/78] ALSA: usb-audio: work around CH345 input SysEx corruption Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 07/78] iio:ad7793: Fix ad7785 product ID Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 01/78] tty: fix stall caused by missing memory barrier in drivers/tty/n_tty.c Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 09/78] ALSA: usb-audio: add packet size quirk for the Medeli DD305 Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100
  [PATCH 3.13.y-ckt 06/78] iio: ad5064: Fix ad5629/ad5669 shift Kamal Mostafa <kamal@canonical.com> - 2015-12-17 02:20 +0100

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