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From:   Kristen Carlson Accardi <kristen@linux.intel.com>
To:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        arjan@linux.intel.com, keescook@chromium.org
Cc:     rick.p.edgecombe@intel.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com,
        Kristen Carlson Accardi <kristen@linux.intel.com>
Subject: [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR
Date:   Wed,  5 Feb 2020 14:39:44 -0800
Message-Id: <20200205223950.1212394-6-kristen@linux.intel.com>
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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@linux.intel.com>
---
 Makefile         |  4 ++++
 arch/x86/Kconfig | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/Makefile b/Makefile
index c50ef91f6136..41438a921666 100644
--- a/Makefile
+++ b/Makefile
@@ -846,6 +846,10 @@ 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 5e8949953660..b4b1b17076a8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2208,6 +2208,19 @@ config RANDOMIZE_BASE
 
 	  If unsure, say Y.
 
+config FG_KASLR
+	bool "Finer grained 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
-- 
2.24.1