linux-dev/security/Kconfig.hardening, branch linus/master

randstruct: Enable Clang support

2022-05-08T08:33:07Z

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: linux-kbuild@vger.kernel.org Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220503205503.3054173-7-keescook@chromium.org

randstruct: Move seed generation into scripts/basic/

2022-05-08T08:33:07Z

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: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220503205503.3054173-6-keescook@chromium.org

randstruct: Reorganize Kconfigs and attribute macros

2022-05-08T08:33:06Z

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: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220503205503.3054173-4-keescook@chromium.org

gcc-plugins/stackleak: Provide verbose mode

2022-02-06T18:49:57Z

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

gcc-plugins: Explicitly document purpose and deprecation schedule

2021-10-21T15:41:38Z

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: linux-hardening@vger.kernel.org Cc: linux-kbuild@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-security-module@vger.kernel.org Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook Reviewed-by: Nathan Chancellor Reviewed-by: Miguel Ojeda Acked-by: Nick Desaulniers Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20211020173554.38122-2-keescook@chromium.org

hardening: Avoid harmless Clang option under CONFIG_INIT_STACK_ALL_ZERO

2021-09-25T15:22:59Z

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] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=a25e0b5e6ac8a77a71c229e0a7b744603365b0e9 Cc: Greg Kroah-Hartman Cc: Masahiro Yamada Cc: llvm@lists.linux.dev Fixes: dcb7c0b9461c ("hardening: Clarify Kconfig text for auto-var-init") Suggested-by: Will Deacon Link: https://lore.kernel.org/lkml/20210914102837.6172-1-will@kernel.org/ Reviewed-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Acked-by: Will Deacon Signed-off-by: Kees Cook

hardening: Clarify Kconfig text for auto-var-init

2021-07-21T06:02:59Z

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: glider@google.com Cc: Nathan Chancellor Cc: Nick Desaulniers Cc: linux-security-module@vger.kernel.org Cc: clang-built-linux@googlegroups.com Signed-off-by: Kees Cook Acked-by: Gustavo A. R. Silva

hardening: Introduce CONFIG_ZERO_CALL_USED_REGS

2021-07-20T22:10:42Z

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%: $ ROPgadget.py --nosys --nojop --binary vmlinux.stock | tail -n1 Unique gadgets found: 337245 $ ROPgadget.py --nosys --nojop --binary vmlinux.zero-call-regs | tail -n1 Unique gadgets found: 267175 and more notably removes simple "write-what-where" gadgets: $ ROPgadget.py --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 $ ROPgadget.py --ropchain --binary vmlinux.zero* | 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 vmlinux.zero-call-regs text data bss dec hex filename 22437676 8559152 14127340 45124168 2b08a48 vmlinux.stock 22453184 8563248 14110956 45127388 2b096dc vmlinux.zero-call-regs 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: https://lore.kernel.org/lkml/20210510134503.GA88495@C02TD0UTHF1T.local/ Signed-off-by: Kees Cook

kasan: remove redundant config option

2021-04-16T23:10:36Z

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] [akpm@linux-foundation.org: fix merge snafu] Link: https://bugzilla.kernel.org/show_bug.cgi?id=210221 [1] Link: https://lkml.kernel.org/r/20210226012531.29231-1-walter-zh.wu@mediatek.com 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

security: allow using Clang's zero initialization for stack variables

2020-06-16T09:06:23Z

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 https://bugs.llvm.org/show_bug.cgi?id=45497). 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: https://lore.kernel.org/r/20200616083435.223038-1-glider@google.com Reviewed-by: Maciej Żenczykowski Signed-off-by: Kees Cook