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* [PATCH 1/3] retpolines: Only enable retpoline when compiler support it
@ 2018-10-30  6:55 Zhenzhong Duan
  2018-10-30  8:32 ` Peter Zijlstra
  2018-10-30  9:39 ` Masahiro Yamada
  0 siblings, 2 replies; 6+ messages in thread
From: Zhenzhong Duan @ 2018-10-30  6:55 UTC (permalink / raw)
  To: Linux-Kernel
  Cc: mingo, luto, konrad.wilk, dwmw, tglx, Srinivas REDDY Eeda, bp,
	daniel, yamada.masahiro, michal.lkml, peterz, hpa

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@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
---
 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

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2018-10-31  5:55 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-30  6:55 [PATCH 1/3] retpolines: Only enable retpoline when compiler support it Zhenzhong Duan
2018-10-30  8:32 ` Peter Zijlstra
2018-10-31  4:58   ` Zhenzhong Duan
2018-10-30  9:39 ` Masahiro Yamada
2018-10-30 10:09   ` Peter Zijlstra
2018-10-31  5:55     ` Zhenzhong Duan

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