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Makefile: introduce CONFIG_CC_STACKPROTECTOR_AUTO

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Nearly all modern compilers support a stack-protector option, and nearly
all modern distributions enable the kernel stack-protector, so enabling
this by default in kernel builds would make sense.  However, Kconfig does
not have knowledge of available compiler features, so it isn't safe to
force on, as this would unconditionally break builds for the compilers or
architectures that don't have support.  Instead, this introduces a new
option, CONFIG_CC_STACKPROTECTOR_AUTO, which attempts to discover the best
possible stack-protector available, and will allow builds to proceed even
if the compiler doesn't support any stack-protector.

This option is made the default so that kernels built with modern
compilers will be protected-by-default against stack buffer overflows,
avoiding things like the recent BlueBorne attack.  Selection of a specific
stack-protector option remains available, including disabling it.

Additionally, tiny.config is adjusted to use CC_STACKPROTECTOR_NONE, since
that's the option with the least code size (and it used to be the default,
so we have to explicitly choose it there now).

Link: http://lkml.kernel.org/r/1510076320-69931-4-git-send-email-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook
2018-02-06 15:37:45 -08:00
committed by Linus Torvalds
parent 2bc2f688fd
commit 44c6dc940b
3 changed files with 45 additions and 4 deletions
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8
arch/Kconfig
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@@ -541,7 +541,7 @@ config HAVE_CC_STACKPROTECTOR
choice
prompt "Stack Protector buffer overflow detection"
depends on HAVE_CC_STACKPROTECTOR
default CC_STACKPROTECTOR_NONE
default CC_STACKPROTECTOR_AUTO
help
This option turns on the "stack-protector" GCC feature. This
feature puts, at the beginning of functions, a canary value on
@@ -588,6 +588,12 @@ config CC_STACKPROTECTOR_STRONG
about 20% of all kernel functions, which increases the kernel code
size by about 2%.
config CC_STACKPROTECTOR_AUTO
bool "Automatic"
help
If the compiler supports it, the best available stack-protector
option will be chosen.
endchoice
config THIN_ARCHIVES