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Date: Thu, 21 May 2020 13:00:12 -0700
From: Kees Cook <keescook@...omium.org>
To: Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
Masahiro Yamada <masahiroy@...nel.org>,
Michal Marek <michal.lkml@...kovi.net>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, arjan@...ux.intel.com,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
rick.p.edgecombe@...el.com, Tony Luck <tony.luck@...el.com>,
linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2 4/9] x86: Makefile: Add build and config option for
CONFIG_FG_KASLR
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 <kristen@...ux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Tested-by: Tony Luck <tony.luck@...el.com>
> ---
> 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 <keescook@...omium.org>
--
Kees Cook
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