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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 188sm5122610pfu.165.2020.05.21.13.00.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2020 13:00:14 -0700 (PDT) Date: Thu, 21 May 2020 13:00:12 -0700 From: Kees Cook To: Kristen Carlson Accardi Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, Masahiro Yamada , Michal Marek , x86@kernel.org, "H. Peter Anvin" , arjan@linux.intel.com, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, rick.p.edgecombe@intel.com, Tony Luck , linux-kbuild@vger.kernel.org Subject: Re: [PATCH v2 4/9] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Message-ID: <202005211255.33E27D05@keescook> References: <20200521165641.15940-1-kristen@linux.intel.com> <20200521165641.15940-5-kristen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200521165641.15940-5-kristen@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 21, 2020 at 09:56:35AM -0700, Kristen Carlson Accardi wrote: > Allow user to select CONFIG_FG_KASLR if dependencies are met. Change > the make file to build with -ffunction-sections if CONFIG_FG_KASLR > > Signed-off-by: Kristen Carlson Accardi > Reviewed-by: Tony Luck > Tested-by: Tony Luck > --- > Makefile | 4 ++++ > arch/x86/Kconfig | 13 +++++++++++++ > 2 files changed, 17 insertions(+) > > diff --git a/Makefile b/Makefile > index 04f5662ae61a..28e515baa824 100644 > --- a/Makefile > +++ b/Makefile > @@ -862,6 +862,10 @@ ifdef CONFIG_LIVEPATCH > KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone) > endif > > +ifdef CONFIG_FG_KASLR > +KBUILD_CFLAGS += -ffunction-sections > +endif > + > # arch Makefile may override CC so keep this after arch Makefile is included > NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 2d3f963fd6f1..50e83ea57d70 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -2183,6 +2183,19 @@ config RANDOMIZE_BASE > > If unsure, say Y. > > +config FG_KASLR > + bool "Function Granular Kernel Address Space Layout Randomization" > + depends on $(cc-option, -ffunction-sections) > + depends on RANDOMIZE_BASE && X86_64 > + help > + This option improves the randomness of the kernel text > + over basic Kernel Address Space Layout Randomization (KASLR) > + by reordering the kernel text at boot time. This feature > + uses information generated at compile time to re-layout the > + kernel text section at boot time at function level granularity. > + > + If unsure, say N. > + > # Relocation on x86 needs some additional build support > config X86_NEED_RELOCS > def_bool y Kconfig bikeshedding: how about putting FG_KASLR in arch/Kconfig, add a "depends on ARCH_HAS_FG_KASLR", and remove the arch-specific depends. Then in arch/x86 have ARCH_HAS_FG_KASLR as a def_bool y with the RANDOMIZE_BASE && X86_64 depends. This will more cleanly split the build elements (compiler flags) from the arch elements (64-bit x86, arch-specific flags, etc). With that split out: Reviewed-by: Kees Cook -- Kees Cook