Commit 2d60d96b authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'meminit-v5.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux 

Pull compiler-based variable initialization updates from Kees Cook:
 "This is effectively part of my gcc-plugins tree, but as this adds some
  Clang support, it felt weird to still call it "gcc-plugins". :)

  This consolidates Kconfig for the existing stack variable
  initialization (via structleak and stackleak gcc plugins) and adds
  Alexander Potapenko's support for Clang's new similar functionality.

  Summary:

   - Consolidate memory initialization Kconfigs (Kees)

   - Implement support for Clang's stack variable auto-init (Alexander)"

* tag 'meminit-v5.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  security: Implement Clang's stack initialization
  security: Move stackleak config to Kconfig.hardening
  security: Create "kernel hardening" config area
parents eac7078a 709a972e

Makefile

+5 −0
Original line number Diff line number Diff line
@@ -748,6 +748,11 @@ KBUILD_CFLAGS += -fomit-frame-pointer 
endif

endif



# Initialize all stack variables with a pattern, if desired.

ifdef CONFIG_INIT_STACK_ALL

KBUILD_CFLAGS	+= -ftrivial-auto-var-init=pattern

endif



DEBUG_CFLAGS	:= $(call cc-option, -fno-var-tracking-assignments)



ifdef CONFIG_DEBUG_INFO

scripts/gcc-plugins/Kconfig

+6 −120
Original line number Diff line number Diff line
@@ -13,17 +13,19 @@ config HAVE_GCC_PLUGINS 
	  An arch should select this symbol if it supports building with

	  GCC plugins.



menuconfig GCC_PLUGINS

	bool "GCC plugins"

config GCC_PLUGINS

	bool

	depends on HAVE_GCC_PLUGINS

	depends on PLUGIN_HOSTCC != ""

	default y

	help

	  GCC plugins are loadable modules that provide extra features to the

	  compiler. They are useful for runtime instrumentation and static analysis.



	  See Documentation/gcc-plugins.txt for details.



if GCC_PLUGINS

menu "GCC plugins"

	depends on GCC_PLUGINS



config GCC_PLUGIN_CYC_COMPLEXITY

	bool "Compute the cyclomatic complexity of a function" if EXPERT
@@ -66,71 +68,6 @@ config GCC_PLUGIN_LATENT_ENTROPY 
	   * https://grsecurity.net/

	   * https://pax.grsecurity.net/



config GCC_PLUGIN_STRUCTLEAK

	bool "Zero initialize stack variables"

	help

	  While the kernel is built with warnings enabled for any missed

	  stack variable initializations, this warning is silenced for

	  anything passed by reference to another function, under the

	  occasionally misguided assumption that the function will do

	  the initialization. As this regularly leads to exploitable

	  flaws, this plugin is available to identify and zero-initialize

	  such variables, depending on the chosen level of coverage.



	  This plugin was originally ported from grsecurity/PaX. More

	  information at:

	   * https://grsecurity.net/

	   * https://pax.grsecurity.net/



choice

	prompt "Coverage"

	depends on GCC_PLUGIN_STRUCTLEAK

	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL

	help

	  This chooses the level of coverage over classes of potentially

	  uninitialized variables. The selected class will be

	  zero-initialized before use.



	config GCC_PLUGIN_STRUCTLEAK_USER

		bool "structs marked for userspace"

		help

		  Zero-initialize any structures on the stack containing

		  a __user attribute. This can prevent some classes of

		  uninitialized stack variable exploits and information

		  exposures, like CVE-2013-2141:

		  https://git.kernel.org/linus/b9e146d8eb3b9eca



	config GCC_PLUGIN_STRUCTLEAK_BYREF

		bool "structs passed by reference"

		help

		  Zero-initialize any structures on the stack that may

		  be passed by reference and had not already been

		  explicitly initialized. This can prevent most classes

		  of uninitialized stack variable exploits and information

		  exposures, like CVE-2017-1000410:

		  https://git.kernel.org/linus/06e7e776ca4d3654



	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL

		bool "anything passed by reference"

		help

		  Zero-initialize any stack variables that may be passed

		  by reference and had not already been explicitly

		  initialized. This is intended to eliminate all classes

		  of uninitialized stack variable exploits and information

		  exposures.



endchoice



config GCC_PLUGIN_STRUCTLEAK_VERBOSE

	bool "Report forcefully initialized variables"

	depends on GCC_PLUGIN_STRUCTLEAK

	depends on !COMPILE_TEST	# too noisy

	help

	  This option will cause a warning to be printed each time the

	  structleak plugin finds a variable it thinks needs to be

	  initialized. Since not all existing initializers are detected

	  by the plugin, this can produce false positive warnings.



config GCC_PLUGIN_RANDSTRUCT

	bool "Randomize layout of sensitive kernel structures"

	select MODVERSIONS if MODULES
@@ -171,59 +108,8 @@ config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE 
	  in structures.  This reduces the performance hit of RANDSTRUCT

	  at the cost of weakened randomization.



config GCC_PLUGIN_STACKLEAK

	bool "Erase the kernel stack before returning from syscalls"

	depends on GCC_PLUGINS

	depends on HAVE_ARCH_STACKLEAK

	help

	  This option makes the kernel erase the kernel stack before

	  returning from system calls. That reduces the information which

	  kernel stack leak bugs can reveal and blocks some uninitialized

	  stack variable attacks.



	  The tradeoff is the performance impact: on a single CPU system kernel

	  compilation sees a 1% slowdown, other systems and workloads may vary

	  and you are advised to test this feature on your expected workload

	  before deploying it.



	  This plugin was ported from grsecurity/PaX. More information at:

	   * https://grsecurity.net/

	   * https://pax.grsecurity.net/



config STACKLEAK_TRACK_MIN_SIZE

	int "Minimum stack frame size of functions tracked by STACKLEAK"

	default 100

	range 0 4096

	depends on GCC_PLUGIN_STACKLEAK

	help

	  The STACKLEAK gcc plugin instruments the kernel code for tracking

	  the lowest border of the kernel stack (and for some other purposes).

	  It inserts the stackleak_track_stack() call for the functions with

	  a stack frame size greater than or equal to this parameter.

	  If unsure, leave the default value 100.



config STACKLEAK_METRICS

	bool "Show STACKLEAK metrics in the /proc file system"

	depends on GCC_PLUGIN_STACKLEAK

	depends on PROC_FS

	help

	  If this is set, STACKLEAK metrics for every task are available in

	  the /proc file system. In particular, /proc/<pid>/stack_depth

	  shows the maximum kernel stack consumption for the current and

	  previous syscalls. Although this information is not precise, it

	  can be useful for estimating the STACKLEAK performance impact for

	  your workloads.



config STACKLEAK_RUNTIME_DISABLE

	bool "Allow runtime disabling of kernel stack erasing"

	depends on GCC_PLUGIN_STACKLEAK

	help

	  This option provides 'stack_erasing' sysctl, which can be used in

	  runtime to control kernel stack erasing for kernels built with

	  CONFIG_GCC_PLUGIN_STACKLEAK.



config GCC_PLUGIN_ARM_SSP_PER_TASK

	bool

	depends on GCC_PLUGINS && ARM



endif
 
endmenu

security/Kconfig

+2 −0
Original line number Diff line number Diff line
@@ -287,5 +287,7 @@ config LSM 


	  If unsure, leave this as the default.



source "security/Kconfig.hardening"



endmenu

security/Kconfig.hardening

0 → 100644
+164 −0
Original line number Diff line number Diff line 
menu "Kernel hardening options"



config GCC_PLUGIN_STRUCTLEAK

	bool

	help

	  While the kernel is built with warnings enabled for any missed

	  stack variable initializations, this warning is silenced for

	  anything passed by reference to another function, under the

	  occasionally misguided assumption that the function will do

	  the initialization. As this regularly leads to exploitable

	  flaws, this plugin is available to identify and zero-initialize

	  such variables, depending on the chosen level of coverage.



	  This plugin was originally ported from grsecurity/PaX. More

	  information at:

	   * https://grsecurity.net/

	   * https://pax.grsecurity.net/



menu "Memory initialization"



config CC_HAS_AUTO_VAR_INIT

	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)



choice

	prompt "Initialize kernel stack variables at function entry"

	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS

	default INIT_STACK_ALL if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT

	default INIT_STACK_NONE

	help

	  This option enables initialization of stack variables at

	  function entry time. This has the possibility to have the

	  greatest coverage (since all functions can have their

	  variables initialized), but the performance impact depends

	  on the function calling complexity of a given workload's

	  syscalls.



	  This chooses the level of coverage over classes of potentially

	  uninitialized variables. The selected class will be

	  initialized before use in a function.



	config INIT_STACK_NONE

		bool "no automatic initialization (weakest)"

		help

		  Disable automatic stack variable initialization.

		  This leaves the kernel vulnerable to the standard

		  classes of uninitialized stack variable exploits

		  and information exposures.



	config GCC_PLUGIN_STRUCTLEAK_USER

		bool "zero-init structs marked for userspace (weak)"

		depends on GCC_PLUGINS

		select GCC_PLUGIN_STRUCTLEAK

		help

		  Zero-initialize any structures on the stack containing

		  a __user attribute. This can prevent some classes of

		  uninitialized stack variable exploits and information

		  exposures, like CVE-2013-2141:

		  https://git.kernel.org/linus/b9e146d8eb3b9eca



	config GCC_PLUGIN_STRUCTLEAK_BYREF

		bool "zero-init structs passed by reference (strong)"

		depends on GCC_PLUGINS

		select GCC_PLUGIN_STRUCTLEAK

		help

		  Zero-initialize any structures on the stack that may

		  be passed by reference and had not already been

		  explicitly initialized. This can prevent most classes

		  of uninitialized stack variable exploits and information

		  exposures, like CVE-2017-1000410:

		  https://git.kernel.org/linus/06e7e776ca4d3654



	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL

		bool "zero-init anything passed by reference (very strong)"

		depends on GCC_PLUGINS

		select GCC_PLUGIN_STRUCTLEAK

		help

		  Zero-initialize any stack variables that may be passed

		  by reference and had not already been explicitly

		  initialized. This is intended to eliminate all classes

		  of uninitialized stack variable exploits and information

		  exposures.



	config INIT_STACK_ALL

		bool "0xAA-init everything on the stack (strongest)"

		depends on CC_HAS_AUTO_VAR_INIT

		help

		  Initializes everything on the stack with a 0xAA

		  pattern. This is intended to eliminate all classes

		  of uninitialized stack variable exploits and information

		  exposures, even variables that were warned to have been

		  left uninitialized.



endchoice



config GCC_PLUGIN_STRUCTLEAK_VERBOSE

	bool "Report forcefully initialized variables"

	depends on GCC_PLUGIN_STRUCTLEAK

	depends on !COMPILE_TEST	# too noisy

	help

	  This option will cause a warning to be printed each time the

	  structleak plugin finds a variable it thinks needs to be

	  initialized. Since not all existing initializers are detected

	  by the plugin, this can produce false positive warnings.



config GCC_PLUGIN_STACKLEAK

	bool "Poison kernel stack before returning from syscalls"

	depends on GCC_PLUGINS

	depends on HAVE_ARCH_STACKLEAK

	help

	  This option makes the kernel erase the kernel stack before

	  returning from system calls. This has the effect of leaving

	  the stack initialized to the poison value, which both reduces

	  the lifetime of any sensitive stack contents and reduces

	  potential for uninitialized stack variable exploits or information

	  exposures (it does not cover functions reaching the same stack

	  depth as prior functions during the same syscall). This blocks

	  most uninitialized stack variable attacks, with the performance

	  impact being driven by the depth of the stack usage, rather than

	  the function calling complexity.



	  The performance impact on a single CPU system kernel compilation

	  sees a 1% slowdown, other systems and workloads may vary and you

	  are advised to test this feature on your expected workload before

	  deploying it.



	  This plugin was ported from grsecurity/PaX. More information at:

	   * https://grsecurity.net/

	   * https://pax.grsecurity.net/



config STACKLEAK_TRACK_MIN_SIZE

	int "Minimum stack frame size of functions tracked by STACKLEAK"

	default 100

	range 0 4096

	depends on GCC_PLUGIN_STACKLEAK

	help

	  The STACKLEAK gcc plugin instruments the kernel code for tracking

	  the lowest border of the kernel stack (and for some other purposes).

	  It inserts the stackleak_track_stack() call for the functions with

	  a stack frame size greater than or equal to this parameter.

	  If unsure, leave the default value 100.



config STACKLEAK_METRICS

	bool "Show STACKLEAK metrics in the /proc file system"

	depends on GCC_PLUGIN_STACKLEAK

	depends on PROC_FS

	help

	  If this is set, STACKLEAK metrics for every task are available in

	  the /proc file system. In particular, /proc/<pid>/stack_depth

	  shows the maximum kernel stack consumption for the current and

	  previous syscalls. Although this information is not precise, it

	  can be useful for estimating the STACKLEAK performance impact for

	  your workloads.



config STACKLEAK_RUNTIME_DISABLE

	bool "Allow runtime disabling of kernel stack erasing"

	depends on GCC_PLUGIN_STACKLEAK

	help

	  This option provides 'stack_erasing' sysctl, which can be used in

	  runtime to control kernel stack erasing for kernels built with

	  CONFIG_GCC_PLUGIN_STACKLEAK.



endmenu



endmenu

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