security/Kconfig.hardening

   1 # SPDX-License-Identifier: GPL-2.0-only
   2 menu "Kernel hardening options"
   3
   4 config GCC_PLUGIN_STRUCTLEAK
   5         bool
   6         help
   7           While the kernel is built with warnings enabled for any missed
   8           stack variable initializations, this warning is silenced for
   9           anything passed by reference to another function, under the
  10           occasionally misguided assumption that the function will do
  11           the initialization. As this regularly leads to exploitable
  12           flaws, this plugin is available to identify and zero-initialize
  13           such variables, depending on the chosen level of coverage.
  14
  15           This plugin was originally ported from grsecurity/PaX. More
  16           information at:
  17            * https://grsecurity.net/
  18            * https://pax.grsecurity.net/
  19
  20 menu "Memory initialization"
  21
  22 config CC_HAS_AUTO_VAR_INIT
  23         def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
  24
  25 choice
  26         prompt "Initialize kernel stack variables at function entry"
  27         default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
  28         default INIT_STACK_ALL if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT
  29         default INIT_STACK_NONE
  30         help
  31           This option enables initialization of stack variables at
  32           function entry time. This has the possibility to have the
  33           greatest coverage (since all functions can have their
  34           variables initialized), but the performance impact depends
  35           on the function calling complexity of a given workload's
  36           syscalls.
  37
  38           This chooses the level of coverage over classes of potentially
  39           uninitialized variables. The selected class will be
  40           initialized before use in a function.
  41
  42         config INIT_STACK_NONE
  43                 bool "no automatic initialization (weakest)"
  44                 help
  45                   Disable automatic stack variable initialization.
  46                   This leaves the kernel vulnerable to the standard
  47                   classes of uninitialized stack variable exploits
  48                   and information exposures.
  49
  50         config GCC_PLUGIN_STRUCTLEAK_USER
  51                 bool "zero-init structs marked for userspace (weak)"
  52                 depends on GCC_PLUGINS
  53                 select GCC_PLUGIN_STRUCTLEAK
  54                 help
  55                   Zero-initialize any structures on the stack containing
  56                   a __user attribute. This can prevent some classes of
  57                   uninitialized stack variable exploits and information
  58                   exposures, like CVE-2013-2141:
  59                   https://git.kernel.org/linus/b9e146d8eb3b9eca
  60
  61         config GCC_PLUGIN_STRUCTLEAK_BYREF
  62                 bool "zero-init structs passed by reference (strong)"
  63                 depends on GCC_PLUGINS
  64                 depends on !(KASAN && KASAN_STACK=1)
  65                 select GCC_PLUGIN_STRUCTLEAK
  66                 help
  67                   Zero-initialize any structures on the stack that may
  68                   be passed by reference and had not already been
  69                   explicitly initialized. This can prevent most classes
  70                   of uninitialized stack variable exploits and information
  71                   exposures, like CVE-2017-1000410:
  72                   https://git.kernel.org/linus/06e7e776ca4d3654
  73
  74                   As a side-effect, this keeps a lot of variables on the
  75                   stack that can otherwise be optimized out, so combining
  76                   this with CONFIG_KASAN_STACK can lead to a stack overflow
  77                   and is disallowed.
  78
  79         config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
  80                 bool "zero-init anything passed by reference (very strong)"
  81                 depends on GCC_PLUGINS
  82                 depends on !(KASAN && KASAN_STACK=1)
  83                 select GCC_PLUGIN_STRUCTLEAK
  84                 help
  85                   Zero-initialize any stack variables that may be passed
  86                   by reference and had not already been explicitly
  87                   initialized. This is intended to eliminate all classes
  88                   of uninitialized stack variable exploits and information
  89                   exposures.
  90
  91         config INIT_STACK_ALL
  92                 bool "0xAA-init everything on the stack (strongest)"
  93                 depends on CC_HAS_AUTO_VAR_INIT
  94                 help
  95                   Initializes everything on the stack with a 0xAA
  96                   pattern. This is intended to eliminate all classes
  97                   of uninitialized stack variable exploits and information
  98                   exposures, even variables that were warned to have been
  99                   left uninitialized.
 100
 101 endchoice
 102
 103 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 104         bool "Report forcefully initialized variables"
 105         depends on GCC_PLUGIN_STRUCTLEAK
 106         depends on !COMPILE_TEST        # too noisy
 107         help
 108           This option will cause a warning to be printed each time the
 109           structleak plugin finds a variable it thinks needs to be
 110           initialized. Since not all existing initializers are detected
 111           by the plugin, this can produce false positive warnings.
 112
 113 config GCC_PLUGIN_STACKLEAK
 114         bool "Poison kernel stack before returning from syscalls"
 115         depends on GCC_PLUGINS
 116         depends on HAVE_ARCH_STACKLEAK
 117         help
 118           This option makes the kernel erase the kernel stack before
 119           returning from system calls. This has the effect of leaving
 120           the stack initialized to the poison value, which both reduces
 121           the lifetime of any sensitive stack contents and reduces
 122           potential for uninitialized stack variable exploits or information
 123           exposures (it does not cover functions reaching the same stack
 124           depth as prior functions during the same syscall). This blocks
 125           most uninitialized stack variable attacks, with the performance
 126           impact being driven by the depth of the stack usage, rather than
 127           the function calling complexity.
 128
 129           The performance impact on a single CPU system kernel compilation
 130           sees a 1% slowdown, other systems and workloads may vary and you
 131           are advised to test this feature on your expected workload before
 132           deploying it.
 133
 134           This plugin was ported from grsecurity/PaX. More information at:
 135            * https://grsecurity.net/
 136            * https://pax.grsecurity.net/
 137
 138 config STACKLEAK_TRACK_MIN_SIZE
 139         int "Minimum stack frame size of functions tracked by STACKLEAK"
 140         default 100
 141         range 0 4096
 142         depends on GCC_PLUGIN_STACKLEAK
 143         help
 144           The STACKLEAK gcc plugin instruments the kernel code for tracking
 145           the lowest border of the kernel stack (and for some other purposes).
 146           It inserts the stackleak_track_stack() call for the functions with
 147           a stack frame size greater than or equal to this parameter.
 148           If unsure, leave the default value 100.
 149
 150 config STACKLEAK_METRICS
 151         bool "Show STACKLEAK metrics in the /proc file system"
 152         depends on GCC_PLUGIN_STACKLEAK
 153         depends on PROC_FS
 154         help
 155           If this is set, STACKLEAK metrics for every task are available in
 156           the /proc file system. In particular, /proc/<pid>/stack_depth
 157           shows the maximum kernel stack consumption for the current and
 158           previous syscalls. Although this information is not precise, it
 159           can be useful for estimating the STACKLEAK performance impact for
 160           your workloads.
 161
 162 config STACKLEAK_RUNTIME_DISABLE
 163         bool "Allow runtime disabling of kernel stack erasing"
 164         depends on GCC_PLUGIN_STACKLEAK
 165         help
 166           This option provides 'stack_erasing' sysctl, which can be used in
 167           runtime to control kernel stack erasing for kernels built with
 168           CONFIG_GCC_PLUGIN_STACKLEAK.
 169
 170 config INIT_ON_ALLOC_DEFAULT_ON
 171         bool "Enable heap memory zeroing on allocation by default"
 172         help
 173           This has the effect of setting "init_on_alloc=1" on the kernel
 174           command line. This can be disabled with "init_on_alloc=0".
 175           When "init_on_alloc" is enabled, all page allocator and slab
 176           allocator memory will be zeroed when allocated, eliminating
 177           many kinds of "uninitialized heap memory" flaws, especially
 178           heap content exposures. The performance impact varies by
 179           workload, but most cases see <1% impact. Some synthetic
 180           workloads have measured as high as 7%.
 181
 182 config INIT_ON_FREE_DEFAULT_ON
 183         bool "Enable heap memory zeroing on free by default"
 184         help
 185           This has the effect of setting "init_on_free=1" on the kernel
 186           command line. This can be disabled with "init_on_free=0".
 187           Similar to "init_on_alloc", when "init_on_free" is enabled,
 188           all page allocator and slab allocator memory will be zeroed
 189           when freed, eliminating many kinds of "uninitialized heap memory"
 190           flaws, especially heap content exposures. The primary difference
 191           with "init_on_free" is that data lifetime in memory is reduced,
 192           as anything freed is wiped immediately, making live forensics or
 193           cold boot memory attacks unable to recover freed memory contents.
 194           The performance impact varies by workload, but is more expensive
 195           than "init_on_alloc" due to the negative cache effects of
 196           touching "cold" memory areas. Most cases see 3-5% impact. Some
 197           synthetic workloads have measured as high as 8%.
 198
 199 endmenu
 200
 201 endmenu