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Date:   Thu, 21 May 2020 09:56:35 -0700
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     keescook@...omium.org, 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>
Cc:     arjan@...ux.intel.com, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, linux-kbuild@...r.kernel.org
Subject: [PATCH v2 4/9] x86: Makefile: Add build and config option for CONFIG_FG_KASLR

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
-- 
2.20.1

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