Hi Kees, On Mon, Oct 02, 2017 at 12:20:04PM -0700, Kees Cook wrote: > As described in the final patch: > > 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. I gave this a spin atop of v4.14-rc3 with a few arm64 toolchains I had installed: * Linaro 17.08 GCC 7.1 // strong * Linaro 17.05 GCC 6.1 // strong * Linaro 15.08 GCC 5.1 // strong * Linaro 14.09 GCC 4.9 // strong * Linaro 13.06 GCC 4.8 // none * Linaro 13.01 GCC 4.7 // none AFAICT, the detection is correct, and arm64 toolchains only gained stack protector support in GCC 4.9. I manually tested GCC 4.8 and 4.7, and got: warning: -fstack-protector not supported for this target [enabled by default] ... so that looks good to me. One thing I noticed was taht even when the build system detects no support for stack-protector, it still passes -DCONFIG_CC_STACKPROTECTOR to the toolchain. Is that expected? Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
