[PATCH 1/3] retpolines: Only enable retpoline when compiler support it
From: Zhenzhong Duan
Date: Tue Oct 30 2018 - 02:56:21 EST
Since retpoline capable compilers are widely available, make
CONFIG_RETPOLINE hard depend on it.
Change KBUILD to use CONFIG_RETPOLINE_SUPPORT to avoid conflict with
CONFIG_RETPOLINE which is used by kernel.
With all that stuff, the check of RETPOLINE is changed to
CONFIG_RETPOLINE.
This change is based on suggestion in https://lkml.org/lkml/2018/9/18/1016
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 2 +-
arch/x86/Kconfig | 8 ++++----
arch/x86/Makefile | 5 +++--
arch/x86/entry/vdso/Makefile | 4 ++--
arch/x86/include/asm/nospec-branch.h | 10 ++++++----
arch/x86/kernel/cpu/bugs.c | 2 +-
arch/x86/kernel/vmlinux.lds.S | 2 +-
arch/x86/lib/Makefile | 2 +-
arch/x86/lib/retpoline.S | 2 ++
scripts/Makefile.build | 2 +-
10 files changed, 22 insertions(+), 17 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e129cd8..c26264e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4187,7 +4187,7 @@
Selecting 'on' will, and 'auto' may, choose a
mitigation method at run time according to the
CPU, the available microcode, the setting of the
- CONFIG_RETPOLINE configuration option, and the
+ CONFIG_RETPOLINE_SUPPORT configuration option, and the
compiler with which the kernel was built.
Specific mitigations can also be selected manually:
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cbd5f28..766563f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -433,7 +433,7 @@ config GOLDFISH
def_bool y
depends on X86_GOLDFISH
-config RETPOLINE
+config RETPOLINE_SUPPORT
bool "Avoid speculative indirect branches in kernel"
default y
select STACK_VALIDATION if HAVE_STACK_VALIDATION
@@ -443,9 +443,9 @@ config RETPOLINE
branches. Requires a compiler with -mindirect-branch=thunk-extern
support for full protection. The kernel may run slower.
- Without compiler support, at least indirect branches in assembler
- code are eliminated. Since this includes the syscall entry path,
- it is not entirely pointless.
+ Since retpoline capable compilers are widely available, kernel doesn't
+ use CONFIG_RETPOLINE_SUPPORT directly but use CONFIG_RETPOLINE which
+ is enabled when compiler support retpoline.
config INTEL_RDT
bool "Intel Resource Director Technology support"
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b562e4..7ed35b1 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -221,9 +221,10 @@ KBUILD_CFLAGS += -Wno-sign-compare
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
# Avoid indirect branches in kernel to deal with Spectre
-ifdef CONFIG_RETPOLINE
+ifdef CONFIG_RETPOLINE_SUPPORT
ifneq ($(RETPOLINE_CFLAGS),)
- KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
+ KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DCONFIG_RETPOLINE
+ KBUILD_AFLAGS += -DCONFIG_RETPOLINE
endif
endif
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 141d415..87acde1 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -70,7 +70,7 @@ CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
-fno-omit-frame-pointer -foptimize-sibling-calls \
-DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
-ifdef CONFIG_RETPOLINE
+ifdef CONFIG_RETPOLINE_SUPPORT
ifneq ($(RETPOLINE_VDSO_CFLAGS),)
CFL += $(RETPOLINE_VDSO_CFLAGS)
endif
@@ -145,7 +145,7 @@ KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
-ifdef CONFIG_RETPOLINE
+ifdef CONFIG_RETPOLINE_SUPPORT
ifneq ($(RETPOLINE_VDSO_CFLAGS),)
KBUILD_CFLAGS_32 += $(RETPOLINE_VDSO_CFLAGS)
endif
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 80dc144..8b09cbb 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -162,11 +162,12 @@
_ASM_PTR " 999b\n\t" \
".popsection\n\t"
-#if defined(CONFIG_X86_64) && defined(RETPOLINE)
+#ifdef CONFIG_RETPOLINE
+#ifdef CONFIG_X86_64
/*
- * Since the inline asm uses the %V modifier which is only in newer GCC,
- * the 64-bit one is dependent on RETPOLINE not CONFIG_RETPOLINE.
+ * Inline asm uses the %V modifier which is only in newer GCC
+ * which is ensured when CONFIG_RETPOLINE is defined.
*/
# define CALL_NOSPEC \
ANNOTATE_NOSPEC_ALTERNATIVE \
@@ -181,7 +182,7 @@
X86_FEATURE_RETPOLINE_AMD)
# define THUNK_TARGET(addr) [thunk_target] "r" (addr)
-#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
+#else /* CONFIG_X86_32 */
/*
* For i386 we use the original ret-equivalent retpoline, because
* otherwise we'll run out of registers. We don't care about CET
@@ -211,6 +212,7 @@
X86_FEATURE_RETPOLINE_AMD)
# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
+#endif
#else /* No retpoline for C / inline asm */
# define CALL_NOSPEC "call *%[thunk_target]\n"
# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c37e66e..d0108fb 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -252,7 +252,7 @@ static void __init spec2_print_if_secure(const char *reason)
static inline bool retp_compiler(void)
{
- return __is_defined(RETPOLINE);
+ return __is_defined(CONFIG_RETPOLINE);
}
static inline bool match_option(const char *arg, int arglen, const char *opt)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 0d618ee..07533f7 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -136,7 +136,7 @@ SECTIONS
*(.fixup)
*(.gnu.warning)
-#ifdef CONFIG_RETPOLINE
+#ifdef CONFIG_RETPOLINE_SUPPORT
__indirect_thunk_start = .;
*(.text.__x86.indirect_thunk)
__indirect_thunk_end = .;
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 25a972c..edfa7ab 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -27,7 +27,7 @@ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
lib-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
-lib-$(CONFIG_RETPOLINE) += retpoline.o
+lib-$(CONFIG_RETPOLINE_SUPPORT) += retpoline.o
obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index c909961..81366ad 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -1,5 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0 */
+#ifdef CONFIG_RETPOLINE
#include <linux/stringify.h>
#include <linux/linkage.h>
#include <asm/dwarf2.h>
@@ -46,3 +47,4 @@ GENERATE_THUNK(r13)
GENERATE_THUNK(r14)
GENERATE_THUNK(r15)
#endif
+#endif
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 54da4b0..259d9c6 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -247,7 +247,7 @@ endif
ifdef CONFIG_GCOV_KERNEL
objtool_args += --no-unreachable
endif
-ifdef CONFIG_RETPOLINE
+ifdef CONFIG_RETPOLINE_SUPPORT
ifneq ($(RETPOLINE_CFLAGS),)
objtool_args += --retpoline
endif
--
1.8.3.1