From 8bd51a2ba3c3bb81a693fff17e983d02d914c14c Mon Sep 17 00:00:00 2001 From: Kees Cook <keescook@chromium.org> Date: Wed, 20 Oct 2021 10:35:53 -0700 Subject: [PATCH] gcc-plugins: Explicitly document purpose and deprecation schedule 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 <masahiroy@kernel.org> Cc: Michal Marek <michal.lkml@markovi.net> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: James Morris <jmorris@namei.org> Cc: "Serge E. Hallyn" <serge@hallyn.com> Cc: Nathan Chancellor <nathan@kernel.org> 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 <keescook@chromium.org> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Miguel Ojeda <ojeda@kernel.org> Acked-by: Nick Desaulniers <ndesaulniers@google.com> Acked-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20211020173554.38122-2-keescook@chromium.org --- Documentation/kbuild/gcc-plugins.rst | 26 ++++++++++++++++++++++++++ scripts/gcc-plugins/Kconfig | 4 ++-- security/Kconfig.hardening | 9 ++++++--- 3 files changed, 34 insertions(+), 5 deletions(-) diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst index 3349966f213dc..4b28c7a4032ff 100644 --- a/Documentation/kbuild/gcc-plugins.rst +++ b/Documentation/kbuild/gcc-plugins.rst @@ -32,6 +32,32 @@ This infrastructure was ported from grsecurity [6]_ and PaX [7]_. .. [7] https://pax.grsecurity.net/ +Purpose +======= + +GCC plugins are designed to provide a place to experiment with potential +compiler features that are neither in GCC nor Clang upstream. Once +their utility is proven, the goal is to upstream the feature into GCC +(and Clang), and then to finally remove them from the kernel once the +feature is available in all supported versions of GCC. + +Specifically, new plugins should implement only features that have no +upstream compiler support (in either GCC or Clang). + +When a feature exists in Clang but not GCC, effort should be made to +bring the feature to upstream GCC (rather than just as a kernel-specific +GCC plugin), so the entire ecosystem can benefit from it. + +Similarly, even if a feature provided by a GCC plugin does *not* exist +in Clang, but the feature is proven to be useful, effort should be spent +to upstream the feature to GCC (and Clang). + +After a feature is available in upstream GCC, the plugin will be made +unbuildable for the corresponding GCC version (and later). Once all +kernel-supported versions of GCC provide the feature, the plugin will +be removed from the kernel. + + Files ===== diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig index ab9eb4cbe33a6..7c7ba3b0d3cd6 100644 --- a/scripts/gcc-plugins/Kconfig +++ b/scripts/gcc-plugins/Kconfig @@ -37,6 +37,8 @@ config GCC_PLUGIN_CYC_COMPLEXITY config GCC_PLUGIN_SANCOV bool + # Plugin can be removed once the kernel only supports GCC 6+ + depends on !CC_HAS_SANCOV_TRACE_PC help This plugin inserts a __sanitizer_cov_trace_pc() call at the start of basic blocks. It supports all gcc versions with plugin support (from @@ -83,8 +85,6 @@ config GCC_PLUGIN_RANDSTRUCT the existing seed and will be removed by a make mrproper or make distclean. - Note that the implementation requires gcc 4.7 or newer. - This plugin was ported from grsecurity/PaX. More information at: * https://grsecurity.net/ * https://pax.grsecurity.net/ diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index ded17b8abce2d..d051f8ceefddd 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -56,7 +56,8 @@ choice config GCC_PLUGIN_STRUCTLEAK_USER bool "zero-init structs marked for userspace (weak)" - depends on GCC_PLUGINS + # Plugin can be removed once the kernel only supports GCC 12+ + depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO select GCC_PLUGIN_STRUCTLEAK help Zero-initialize any structures on the stack containing @@ -67,7 +68,8 @@ choice config GCC_PLUGIN_STRUCTLEAK_BYREF bool "zero-init structs passed by reference (strong)" - depends on GCC_PLUGINS + # Plugin can be removed once the kernel only supports GCC 12+ + depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO depends on !(KASAN && KASAN_STACK) select GCC_PLUGIN_STRUCTLEAK help @@ -85,7 +87,8 @@ choice config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL bool "zero-init everything passed by reference (very strong)" - depends on GCC_PLUGINS + # Plugin can be removed once the kernel only supports GCC 12+ + depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO depends on !(KASAN && KASAN_STACK) select GCC_PLUGIN_STRUCTLEAK help -- GitLab