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gcc-plugins: Explicitly document purpose and deprecation schedule

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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
This commit is contained in:
Kees Cook 2021-10-20 10:35:53 -07:00
parent 6eb4bd92c1
commit 8bd51a2ba3
3 changed files with 34 additions and 5 deletions
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26
Documentation/kbuild/gcc-plugins.rst
View File

@ -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
=====

4
scripts/gcc-plugins/Kconfig
View File

@ -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/

9
security/Kconfig.hardening
View File

@ -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