linux-kernel - [PATCH v2] objtool, retpolines: Integrate objtool with retpoline support more closely

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Date:   Wed, 21 Feb 2018 16:55:31 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>, hpa@...or.com,
        luto@...nel.org, arjan@...ux.intel.com, tglx@...utronix.de,
        dan.j.williams@...el.com, torvalds@...ux-foundation.org,
        gregkh@...uxfoundation.org, bp@...en8.de,
        linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
        jpoimboe@...hat.com, linux-tip-commits@...r.kernel.org
Subject: [PATCH v2] objtool, retpolines: Integrate objtool with retpoline
 support more closely


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Feb 21, 2018 at 01:53:57PM +0100, Peter Zijlstra wrote:
> > That's because this crossed with the llvm cruft, right? I'll have a
> > look.
> 
> Best I could come up with that seems to work is something like the
> below. Ingo, can you backmerge or stuff on top as appropriate?

I backmerged/reordered and made the v2 patch below out of it.

Does this look good to everyone?

Thanks,

	Ingo

=======================>
>From d5028ba8ee5a18c9d0bb926d883c28b370f89009 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@...radead.org>
Date: Tue, 6 Feb 2018 09:46:13 +0100
Subject: [PATCH] objtool, retpolines: Integrate objtool with retpoline support more closely

Disable retpoline validation in objtool if your compiler sucks, and otherwise
select the validation stuff for CONFIG_RETPOLINE=y (most builds would already
have it set due to ORC).

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 Makefile               |  5 +++++
 arch/x86/Kconfig       |  1 +
 arch/x86/Makefile      | 10 +++-------
 scripts/Makefile.build |  2 ++
 4 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 79ad2bfa24b6..3dfce4d2f25d 100644
--- a/Makefile
+++ b/Makefile
@@ -489,6 +489,11 @@ KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
 KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
 endif
 
+RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
+RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
+RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
+export RETPOLINE_CFLAGS
+
 ifeq ($(config-targets),1)
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 63bf349b2b24..c1aed6c0e413 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -436,6 +436,7 @@ config GOLDFISH
 config RETPOLINE
 	bool "Avoid speculative indirect branches in kernel"
 	default y
+	select STACK_VALIDATION if HAVE_STACK_VALIDATION
 	help
 	  Compile kernel with the retpoline compiler options to guard against
 	  kernel-to-user data leaks by avoiding speculative indirect
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index dbc7d0ed2eaa..498c1b812300 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -232,13 +232,9 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-    RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
-    RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
-
-    RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
-    ifneq ($(RETPOLINE_CFLAGS),)
-        KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
-    endif
+ifneq ($(RETPOLINE_CFLAGS),)
+  KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
+endif
 endif
 
 archscripts: scripts_basic
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index ce0fc4dd68c6..4f2b25d43ec9 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -267,8 +267,10 @@ else
 objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
 endif
 ifdef CONFIG_RETPOLINE
+ifneq ($(RETPOLINE_CFLAGS),)
   objtool_args += --retpoline
 endif
+endif
 
 
 ifdef CONFIG_MODVERSIONS