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Message-Id: <20200923173905.11219-4-kristen@linux.intel.com>
Date: Wed, 23 Sep 2020 10:38:57 -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>,
Arnd Bergmann <arnd@...db.de>
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,
linux-arch@...r.kernel.org
Subject: [PATCH v5 03/10] 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.
While the only architecture that supports CONFIG_FG_KASLR does not
currently enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION, make sure these
2 features play nicely together for the future by ensuring that if
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is selected when used with
CONFIG_FG_KASLR the function sections will not be consolidated back
into .text. Thanks to Kees Cook for the dead code elimination changes.
Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Tested-by: Tony Luck <tony.luck@...el.com>
---
Makefile | 6 +++++-
arch/x86/Kconfig | 4 ++++
include/asm-generic/vmlinux.lds.h | 16 ++++++++++++++--
init/Kconfig | 14 ++++++++++++++
4 files changed, 37 insertions(+), 3 deletions(-)
diff --git a/Makefile b/Makefile
index 2b66d3398878..0c116b833fd5 100644
--- a/Makefile
+++ b/Makefile
@@ -878,10 +878,14 @@ KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
endif
ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
-KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections
+KBUILD_CFLAGS_KERNEL += -fdata-sections
LDFLAGS_vmlinux += --gc-sections
endif
+ifneq ($(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION)$(CONFIG_FG_KASLR),)
+KBUILD_CFLAGS += -ffunction-sections
+endif
+
ifdef CONFIG_SHADOW_CALL_STACK
CC_FLAGS_SCS := -fsanitize=shadow-call-stack
KBUILD_CFLAGS += $(CC_FLAGS_SCS)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7101ac64bb20..ff0f90d0421f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -374,6 +374,10 @@ config CC_HAS_SANE_STACKPROTECTOR
We have to make sure stack protector is unconditionally disabled if
the compiler produces broken code.
+config ARCH_HAS_FG_KASLR
+ def_bool y
+ depends on RANDOMIZE_BASE && X86_64
+
menu "Processor type and features"
config ZONE_DMA
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5430febd34be..afd5cdf79a3a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -93,14 +93,12 @@
* sections to be brought in with rodata.
*/
#ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
-#define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX*
#define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]*
#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]*
#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]*
#define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]*
#else
-#define TEXT_MAIN .text
#define DATA_MAIN .data
#define SDATA_MAIN .sdata
#define RODATA_MAIN .rodata
@@ -108,6 +106,20 @@
#define SBSS_MAIN .sbss
#endif
+/*
+ * Both LD_DEAD_CODE_DATA_ELIMINATION and CONFIG_FG_KASLR options enable
+ * -ffunction-sections, which produces separately named .text sections. In
+ * the case of CONFIG_FG_KASLR, they need to stay distict so they can be
+ * separately randomized. Without CONFIG_FG_KASLR, the separate .text
+ * sections can be collected back into a common section, which makes the
+ * resulting image slightly smaller
+ */
+#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) && !defined(CONFIG_FG_KASLR)
+#define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
+#else
+#define TEXT_MAIN .text
+#endif
+
/*
* GCC 4.5 and later have a 32 bytes section alignment for structures.
* Except GCC 4.9, that feels the need to align on 64 bytes.
diff --git a/init/Kconfig b/init/Kconfig
index d6a0b31b13dc..81220973b064 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2019,6 +2019,20 @@ config PROFILING
config TRACEPOINTS
bool
+config FG_KASLR
+ bool "Function Granular Kernel Address Space Layout Randomization"
+ depends on $(cc-option, -ffunction-sections)
+ depends on ARCH_HAS_FG_KASLR
+ default n
+ 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.
+
endmenu # General setup
source "arch/Kconfig"
--
2.20.1
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