path: root/security/Kconfig.hardening
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2022-05-08randstruct: Enable Clang supportKees Cook
Clang 15 will support randstruct via the -frandomize-layout-seed-file=... option. Update the Kconfig and Makefile to recognize this feature. Cc: Masahiro Yamada <> Cc: Signed-off-by: Kees Cook <> Link:
2022-05-08randstruct: Move seed generation into scripts/basic/Kees Cook
To enable Clang randstruct support, move the structure layout randomization seed generation out of scripts/gcc-plugins/ into scripts/basic/ so it happens early enough that it can be used by either compiler implementation. The gcc-plugin still builds its own header file, but now does so from the common "randstruct.seed" file. Cc: Signed-off-by: Kees Cook <> Link:
2022-05-08randstruct: Reorganize Kconfigs and attribute macrosKees Cook
In preparation for Clang supporting randstruct, reorganize the Kconfigs, move the attribute macros, and generalize the feature to be named CONFIG_RANDSTRUCT for on/off, CONFIG_RANDSTRUCT_FULL for the full randomization mode, and CONFIG_RANDSTRUCT_PERFORMANCE for the cache-line sized mode. Cc: Signed-off-by: Kees Cook <> Link:
2022-02-06gcc-plugins/stackleak: Provide verbose modeKees Cook
In order to compare instrumentation between builds, make the verbose mode of the plugin available during the build. This is rarely needed (behind EXPERT) and very noisy (disabled for COMPILE_TEST). Cc: Alexander Popov <> Signed-off-by: Kees Cook <>
2021-10-21gcc-plugins: Explicitly document purpose and deprecation scheduleKees Cook
GCC plugins should only exist when some compiler feature needs to be proven but does not exist in either GCC nor Clang. For example, if a desired feature is already in Clang, it should be added to GCC upstream. Document this explicitly. Additionally, mark the plugins with matching upstream GCC features as removable past their respective GCC versions. Cc: Masahiro Yamada <> Cc: Michal Marek <> Cc: Nick Desaulniers <> Cc: Jonathan Corbet <> Cc: James Morris <> Cc: "Serge E. Hallyn" <> Cc: Nathan Chancellor <> Cc: Cc: Cc: Cc: Cc: Signed-off-by: Kees Cook <> Reviewed-by: Nathan Chancellor <> Reviewed-by: Miguel Ojeda <> Acked-by: Nick Desaulniers <> Acked-by: Ard Biesheuvel <> Link:
2021-09-25hardening: Avoid harmless Clang option under CONFIG_INIT_STACK_ALL_ZEROKees Cook
Currently under Clang, CC_HAS_AUTO_VAR_INIT_ZERO requires an extra -enable flag compared to CC_HAS_AUTO_VAR_INIT_PATTERN. GCC 12[1] will not, and will happily ignore the Clang-specific flag. However, its presence on the command-line is both cumbersome and confusing. Due to GCC's tolerant behavior, though, we can continue to use a single Kconfig cc-option test for the feature on both compilers, but then drop the Clang-specific option in the Makefile. In other words, this patch does not change anything other than making the compiler command line shorter once GCC supports -ftrivial-auto-var-init=zero. [1];a=commitdiff;h=a25e0b5e6ac8a77a71c229e0a7b744603365b0e9 Cc: Greg Kroah-Hartman <> Cc: Masahiro Yamada <> Cc: Fixes: dcb7c0b9461c ("hardening: Clarify Kconfig text for auto-var-init") Suggested-by: Will Deacon <> Link: Reviewed-by: Nick Desaulniers <> Reviewed-by: Nathan Chancellor <> Acked-by: Will Deacon <> Signed-off-by: Kees Cook <>
2021-07-20hardening: Clarify Kconfig text for auto-var-initKees Cook
Clarify the details around the automatic variable initialization modes available. Specifically this details the values used for pattern init and expands on the rationale for zero init safety. Additionally makes zero init the default when available. Cc: Cc: Nathan Chancellor <> Cc: Nick Desaulniers <> Cc: Cc: Signed-off-by: Kees Cook <> Acked-by: Gustavo A. R. Silva <>
2021-07-20hardening: Introduce CONFIG_ZERO_CALL_USED_REGSKees Cook
When CONFIG_ZERO_CALL_USED_REGS is enabled, build the kernel with "-fzero-call-used-regs=used-gpr" (in GCC 11). This option will zero any caller-used register contents just before returning from a function, ensuring that temporary values are not leaked beyond the function boundary. This means that register contents are less likely to be available for side channel attacks and information exposures. Additionally this helps reduce the number of useful ROP gadgets in the kernel image by about 20%: $ --nosys --nojop --binary vmlinux.stock | tail -n1 Unique gadgets found: 337245 $ --nosys --nojop --binary | tail -n1 Unique gadgets found: 267175 and more notably removes simple "write-what-where" gadgets: $ --ropchain --binary vmlinux.stock | sed -n '/Step 1/,/Step 2/p' - Step 1 -- Write-what-where gadgets [+] Gadget found: 0xffffffff8102d76c mov qword ptr [rsi], rdx ; ret [+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret [+] Gadget found: 0xffffffff8104d7c8 pop rdx ; ret [-] Can't find the 'xor rdx, rdx' gadget. Try with another 'mov [reg], reg' [+] Gadget found: 0xffffffff814c2b4c mov qword ptr [rsi], rdi ; ret [+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret [+] Gadget found: 0xffffffff81001e51 pop rdi ; ret [-] Can't find the 'xor rdi, rdi' gadget. Try with another 'mov [reg], reg' [+] Gadget found: 0xffffffff81540d61 mov qword ptr [rsi], rdi ; pop rbx ; pop rbp ; ret [+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret [+] Gadget found: 0xffffffff81001e51 pop rdi ; ret [-] Can't find the 'xor rdi, rdi' gadget. Try with another 'mov [reg], reg' [+] Gadget found: 0xffffffff8105341e mov qword ptr [rsi], rax ; ret [+] Gadget found: 0xffffffff81000cf5 pop rsi ; ret [+] Gadget found: 0xffffffff81029a11 pop rax ; ret [+] Gadget found: 0xffffffff811f1c3b xor rax, rax ; ret - Step 2 -- Init syscall number gadgets $ --ropchain --binary* | sed -n '/Step 1/,/Step 2/p' - Step 1 -- Write-what-where gadgets [-] Can't find the 'mov qword ptr [r64], r64' gadget For an x86_64 parallel build tests, this has a less than 1% performance impact, and grows the image size less than 1%: $ size vmlinux.stock text data bss dec hex filename 22437676 8559152 14127340 45124168 2b08a48 vmlinux.stock 22453184 8563248 14110956 45127388 2b096dc Impact for other architectures may vary. For example, arm64 sees a 5.5% image size growth, mainly due to needing to always clear x16 and x17: Signed-off-by: Kees Cook <>
2021-04-16kasan: remove redundant config optionWalter Wu
CONFIG_KASAN_STACK and CONFIG_KASAN_STACK_ENABLE both enable KASAN stack instrumentation, but we should only need one config, so that we remove CONFIG_KASAN_STACK_ENABLE and make CONFIG_KASAN_STACK workable. see [1]. When enable KASAN stack instrumentation, then for gcc we could do no prompt and default value y, and for clang prompt and default value n. This patch fixes the following compilation warning: include/linux/kasan.h:333:30: warning: 'CONFIG_KASAN_STACK' is not defined, evaluates to 0 [-Wundef] [ fix merge snafu] Link: [1] Link: Fixes: d9b571c885a8 ("kasan: fix KASAN_STACK dependency for HW_TAGS") Signed-off-by: Walter Wu <> Suggested-by: Dmitry Vyukov <> Reviewed-by: Nathan Chancellor <> Acked-by: Arnd Bergmann <> Reviewed-by: Andrey Konovalov <> Cc: Andrey Ryabinin <> Cc: Dmitry Vyukov <> Cc: Alexander Potapenko <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
2020-06-16security: allow using Clang's zero initialization for stack
In addition to -ftrivial-auto-var-init=pattern (used by CONFIG_INIT_STACK_ALL now) Clang also supports zero initialization for locals enabled by -ftrivial-auto-var-init=zero. The future of this flag is still being debated (see Right now it is guarded by another flag, -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang, which means it may not be supported by future Clang releases. Another possible resolution is that -ftrivial-auto-var-init=zero will persist (as certain users have already started depending on it), but the name of the guard flag will change. In the meantime, zero initialization has proven itself as a good production mitigation measure against uninitialized locals. Unlike pattern initialization, which has a higher chance of triggering existing bugs, zero initialization provides safe defaults for strings, pointers, indexes, and sizes. On the other hand, pattern initialization remains safer for return values. Chrome OS and Android are moving to using zero initialization for production builds. Performance-wise, the difference between pattern and zero initialization is usually negligible, although the generated code for zero initialization is more compact. This patch renames CONFIG_INIT_STACK_ALL to CONFIG_INIT_STACK_ALL_PATTERN and introduces another config option, CONFIG_INIT_STACK_ALL_ZERO, that enables zero initialization for locals if the corresponding flags are supported by Clang. Cc: Kees Cook <> Cc: Nick Desaulniers <> Cc: Greg Kroah-Hartman <> Signed-off-by: Alexander Potapenko <> Link: Reviewed-by: Maciej Żenczykowski <> Signed-off-by: Kees Cook <>
2019-07-28Merge tag 'meminit-v5.3-rc2' of ↵Linus Torvalds
git:// Pull structleak fix from Kees Cook: "Disable gcc-based stack variable auto-init under KASAN (Arnd Bergmann). This fixes a bunch of build warnings under KASAN and the gcc-plugin-based stack auto-initialization features (which are arguably redundant, so better to let KASAN control this)" * tag 'meminit-v5.3-rc2' of git:// structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK
2019-07-25structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACKArnd Bergmann
The combination of KASAN_STACK and GCC_PLUGIN_STRUCTLEAK_BYREF leads to much larger kernel stack usage, as seen from the warnings about functions that now exceed the 2048 byte limit: drivers/media/i2c/tvp5150.c:253:1: error: the frame size of 3936 bytes is larger than 2048 bytes drivers/media/tuners/r820t.c:1327:1: error: the frame size of 2816 bytes is larger than 2048 bytes drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:16552:1: error: the frame size of 3144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=] fs/ocfs2/aops.c:1892:1: error: the frame size of 2088 bytes is larger than 2048 bytes fs/ocfs2/dlm/dlmrecovery.c:737:1: error: the frame size of 2088 bytes is larger than 2048 bytes fs/ocfs2/namei.c:1677:1: error: the frame size of 2584 bytes is larger than 2048 bytes fs/ocfs2/super.c:1186:1: error: the frame size of 2640 bytes is larger than 2048 bytes fs/ocfs2/xattr.c:3678:1: error: the frame size of 2176 bytes is larger than 2048 bytes net/bluetooth/l2cap_core.c:7056:1: error: the frame size of 2144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=] net/bluetooth/l2cap_core.c: In function 'l2cap_recv_frame': net/bridge/br_netlink.c:1505:1: error: the frame size of 2448 bytes is larger than 2048 bytes net/ieee802154/nl802154.c:548:1: error: the frame size of 2232 bytes is larger than 2048 bytes net/wireless/nl80211.c:1726:1: error: the frame size of 2224 bytes is larger than 2048 bytes net/wireless/nl80211.c:2357:1: error: the frame size of 4584 bytes is larger than 2048 bytes net/wireless/nl80211.c:5108:1: error: the frame size of 2760 bytes is larger than 2048 bytes net/wireless/nl80211.c:6472:1: error: the frame size of 2112 bytes is larger than 2048 bytes The structleak plugin was previously disabled for CONFIG_COMPILE_TEST, but meant we missed some bugs, so this time we should address them. The frame size warnings are distracting, and risking a kernel stack overflow is generally not beneficial to performance, so it may be best to disallow that particular combination. This can be done by turning off either one. I picked the dependency in GCC_PLUGIN_STRUCTLEAK_BYREF and GCC_PLUGIN_STRUCTLEAK_BYREF_ALL, as this option is designed to make uninitialized stack usage less harmful when enabled on its own, but it also prevents KASAN from detecting those cases in which it was in fact needed. KASAN_STACK is currently implied by KASAN on gcc, but could be made a user selectable option if we want to allow combining (non-stack) KASAN with GCC_PLUGIN_STRUCTLEAK_BYREF. Note that it would be possible to specifically address the files that print the warning, but presumably the overall stack usage is still significantly higher than in other configurations, so this would not address the full problem. I could not test this with CONFIG_INIT_STACK_ALL, which may or may not suffer from a similar problem. Fixes: 81a56f6dcd20 ("gcc-plugins: structleak: Generalize to all variable types") Signed-off-by: Arnd Bergmann <> Link: Signed-off-by: Kees Cook <>
2019-07-12mm: security: introduce init_on_alloc=1 and init_on_free=1 boot optionsAlexander Potapenko
Patch series "add init_on_alloc/init_on_free boot options", v10. Provide init_on_alloc and init_on_free boot options. These are aimed at preventing possible information leaks and making the control-flow bugs that depend on uninitialized values more deterministic. Enabling either of the options guarantees that the memory returned by the page allocator and SL[AU]B is initialized with zeroes. SLOB allocator isn't supported at the moment, as its emulation of kmem caches complicates handling of SLAB_TYPESAFE_BY_RCU caches correctly. Enabling init_on_free also guarantees that pages and heap objects are initialized right after they're freed, so it won't be possible to access stale data by using a dangling pointer. As suggested by Michal Hocko, right now we don't let the heap users to disable initialization for certain allocations. There's not enough evidence that doing so can speed up real-life cases, and introducing ways to opt-out may result in things going out of control. This patch (of 2): The new options are needed to prevent possible information leaks and make control-flow bugs that depend on uninitialized values more deterministic. This is expected to be on-by-default on Android and Chrome OS. And it gives the opportunity for anyone else to use it under distros too via the boot args. (The init_on_free feature is regularly requested by folks where memory forensics is included in their threat models.) init_on_alloc=1 makes the kernel initialize newly allocated pages and heap objects with zeroes. Initialization is done at allocation time at the places where checks for __GFP_ZERO are performed. init_on_free=1 makes the kernel initialize freed pages and heap objects with zeroes upon their deletion. This helps to ensure sensitive data doesn't leak via use-after-free accesses. Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator returns zeroed memory. The two exceptions are slab caches with constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never zero-initialized to preserve their semantics. Both init_on_alloc and init_on_free default to zero, but those defaults can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON. If either SLUB poisoning or page poisoning is enabled, those options take precedence over init_on_alloc and init_on_free: initialization is only applied to unpoisoned allocations. Slowdown for the new features compared to init_on_free=0, init_on_alloc=0: hackbench, init_on_free=1: +7.62% sys time (st.err 0.74%) hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%) Linux build with -j12, init_on_free=1: +8.38% wall time (st.err 0.39%) Linux build with -j12, init_on_free=1: +24.42% sys time (st.err 0.52%) Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%) Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%) The slowdown for init_on_free=0, init_on_alloc=0 compared to the baseline is within the standard error. The new features are also going to pave the way for hardware memory tagging (e.g. arm64's MTE), which will require both on_alloc and on_free hooks to set the tags for heap objects. With MTE, tagging will have the same cost as memory initialization. Although init_on_free is rather costly, there are paranoid use-cases where in-memory data lifetime is desired to be minimized. There are various arguments for/against the realism of the associated threat models, but given that we'll need the infrastructure for MTE anyway, and there are people who want wipe-on-free behavior no matter what the performance cost, it seems reasonable to include it in this series. [ v8] Link: [ v9] Link: [ v10] Link: Link: Signed-off-by: Alexander Potapenko <> Acked-by: Kees Cook <> Acked-by: Michal Hocko <> [page and dmapool parts Acked-by: James Morris <>] Cc: Christoph Lameter <> Cc: Masahiro Yamada <> Cc: "Serge E. Hallyn" <> Cc: Nick Desaulniers <> Cc: Kostya Serebryany <> Cc: Dmitry Vyukov <> Cc: Sandeep Patil <> Cc: Laura Abbott <> Cc: Randy Dunlap <> Cc: Jann Horn <> Cc: Mark Rutland <> Cc: Marco Elver <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
2019-05-21treewide: Add SPDX license identifier - Makefile/KconfigThomas Gleixner
Add SPDX license identifiers to all Make/Kconfig files which: - Have no license information of any form These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <> Signed-off-by: Greg Kroah-Hartman <>
2019-04-24security: Implement Clang's stack initializationKees Cook
CONFIG_INIT_STACK_ALL turns on stack initialization based on -ftrivial-auto-var-init in Clang builds, which has greater coverage than CONFIG_GCC_PLUGINS_STRUCTLEAK_BYREF_ALL. -ftrivial-auto-var-init Clang option provides trivial initializers for uninitialized local variables, variable fields and padding. It has three possible values: pattern - uninitialized locals are filled with a fixed pattern (mostly 0xAA on 64-bit platforms, see for more details, but 0x000000AA for 32-bit pointers) likely to cause crashes when uninitialized value is used; zero (it's still debated whether this flag makes it to the official Clang release) - uninitialized locals are filled with zeroes; uninitialized (default) - uninitialized locals are left intact. This patch uses only the "pattern" mode when CONFIG_INIT_STACK_ALL is enabled. Developers have the possibility to opt-out of this feature on a per-variable basis by using __attribute__((uninitialized)), but such use should be well justified in comments. Co-developed-by: Alexander Potapenko <> Signed-off-by: Alexander Potapenko <> Signed-off-by: Kees Cook <> Tested-by: Alexander Potapenko <> Acked-by: Masahiro Yamada <>
2019-04-24security: Move stackleak config to Kconfig.hardeningKees Cook
This moves the stackleak plugin options to Kconfig.hardening's memory initialization menu. Signed-off-by: Kees Cook <> Reviewed-by: Alexander Popov <> Acked-by: Masahiro Yamada <>
2019-04-24security: Create "kernel hardening" config areaKees Cook
Right now kernel hardening options are scattered around various Kconfig files. This can be a central place to collect these kinds of options going forward. This is initially populated with the memory initialization options from the gcc-plugins. Signed-off-by: Kees Cook <> Acked-by: Masahiro Yamada <>