1e860048c5
Linus pointed out a third of the time in the Kconfig parse stage comes
from the single invocation of cc1plus in scripts/gcc-plugin.sh [1],
and directly testing plugin-version.h for existence cuts down the
overhead a lot. [2]
This commit takes one step further to kill the build test entirely.
The small piece of code was probably intended to test the C++ designated
initializer, which was not supported until C++20.
In fact, with -pedantic option given, both GCC and Clang emit a warning.
$ echo 'class test { public: int test; } test = { .test = 1 };' | g++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: C++ designated initializers only available with '-std=c++2a' or '-std=gnu++2a' [-Wpedantic]
$ echo 'class test { public: int test; } test = { .test = 1 };' | clang++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: designated initializers are a C++20 extension [-Wc++20-designator]
class test { public: int test; } test = { .test = 1 };
^
1 warning generated.
Otherwise, modern C++ compilers should be able to build the code, and
hopefully skipping this test should not make any practical problem.
Checking the existence of plugin-version.h is still needed to ensure
the plugin-dev package is installed. The test code is now small enough
to be embedded in scripts/gcc-plugins/Kconfig.
[1] https://lore.kernel.org/lkml/CAHk-=wjU4DCuwQ4pXshRbwDCUQB31ScaeuDo1tjoZ0_PjhLHzQ@mail.gmail.com/
[2] https://lore.kernel.org/lkml/CAHk-=whK0aQxs6Q5ijJmYF1n2ch8cVFSUzU5yUM_HOjig=+vnw@mail.gmail.com/
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201203125700.161354-1-masahiroy@kernel.org
108 lines
3.8 KiB
Plaintext
108 lines
3.8 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config HAVE_GCC_PLUGINS
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bool
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help
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An arch should select this symbol if it supports building with
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GCC plugins.
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menuconfig GCC_PLUGINS
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bool "GCC plugins"
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depends on HAVE_GCC_PLUGINS
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depends on CC_IS_GCC
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depends on $(success,test -e $(shell,$(CC) -print-file-name=plugin)/include/plugin-version.h)
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default y
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help
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GCC plugins are loadable modules that provide extra features to the
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compiler. They are useful for runtime instrumentation and static analysis.
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See Documentation/kbuild/gcc-plugins.rst for details.
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if GCC_PLUGINS
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config GCC_PLUGIN_CYC_COMPLEXITY
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bool "Compute the cyclomatic complexity of a function" if EXPERT
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depends on !COMPILE_TEST # too noisy
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help
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The complexity M of a function's control flow graph is defined as:
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M = E - N + 2P
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where
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E = the number of edges
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N = the number of nodes
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P = the number of connected components (exit nodes).
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Enabling this plugin reports the complexity to stderr during the
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build. It mainly serves as a simple example of how to create a
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gcc plugin for the kernel.
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config GCC_PLUGIN_SANCOV
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bool
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help
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This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
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basic blocks. It supports all gcc versions with plugin support (from
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gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
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by Dmitry Vyukov <dvyukov@google.com>.
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config GCC_PLUGIN_LATENT_ENTROPY
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bool "Generate some entropy during boot and runtime"
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help
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By saying Y here the kernel will instrument some kernel code to
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extract some entropy from both original and artificially created
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program state. This will help especially embedded systems where
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there is little 'natural' source of entropy normally. The cost
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is some slowdown of the boot process (about 0.5%) and fork and
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irq processing.
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Note that entropy extracted this way is not cryptographically
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secure!
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This plugin was ported from grsecurity/PaX. More information at:
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* https://grsecurity.net/
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* https://pax.grsecurity.net/
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config GCC_PLUGIN_RANDSTRUCT
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bool "Randomize layout of sensitive kernel structures"
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select MODVERSIONS if MODULES
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help
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If you say Y here, the layouts of structures that are entirely
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function pointers (and have not been manually annotated with
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__no_randomize_layout), or structures that have been explicitly
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marked with __randomize_layout, will be randomized at compile-time.
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This can introduce the requirement of an additional information
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exposure vulnerability for exploits targeting these structure
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types.
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Enabling this feature will introduce some performance impact,
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slightly increase memory usage, and prevent the use of forensic
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tools like Volatility against the system (unless the kernel
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source tree isn't cleaned after kernel installation).
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The seed used for compilation is located at
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scripts/gcc-plugins/randomize_layout_seed.h. It remains after
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a make clean to allow for external modules to be compiled with
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the existing seed and will be removed by a make mrproper or
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make distclean.
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Note that the implementation requires gcc 4.7 or newer.
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This plugin was ported from grsecurity/PaX. More information at:
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* https://grsecurity.net/
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* https://pax.grsecurity.net/
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config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
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bool "Use cacheline-aware structure randomization"
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depends on GCC_PLUGIN_RANDSTRUCT
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depends on !COMPILE_TEST # do not reduce test coverage
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help
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If you say Y here, the RANDSTRUCT randomization will make a
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best effort at restricting randomization to cacheline-sized
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groups of elements. It will further not randomize bitfields
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in structures. This reduces the performance hit of RANDSTRUCT
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at the cost of weakened randomization.
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config GCC_PLUGIN_ARM_SSP_PER_TASK
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bool
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depends on GCC_PLUGINS && ARM
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endif
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