Re: [PATCH 4.9 02/24] x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support

[Ben Hutchings]

On Wed, 2022-03-09 at 16:59 +0100, Greg Kroah-Hartman wrote:
> From: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> 
> commit 4cd24de3a0980bf3100c9dcb08ef65ca7c31af48 upstream.
[...]

Sorry, there are a couple of fixes needed on top of this:

commit 25896d073d8a0403b07e6dec56f58e6c33678207
Author: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Date:   Wed Dec 5 15:27:19 2018 +0900
 
    x86/build: Fix compiler support check for CONFIG_RETPOLINE

commit e4f358916d528d479c3c12bd2fd03f2d5a576380
Author: WANG Chao <chao.wang@xxxxxxxxx>
Date:   Tue Dec 11 00:37:25 2018 +0800
 
    x86, modpost: Replace last remnants of RETPOLINE with CONFIG_RETPOLINE

I've attached my backports of those.

Ben.

-- 
Ben Hutchings
73.46% of all statistics are made up.
From 37cd19b0e1e70592d3d547360bf979f69514f3c1 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Date: Wed, 5 Dec 2018 15:27:19 +0900
Subject: [PATCH 1/2] x86/build: Fix compiler support check for
 CONFIG_RETPOLINE

commit 25896d073d8a0403b07e6dec56f58e6c33678207 upstream.

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like
this commit did:

  829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler")

Reported-by: Meelis Roos <mroos@xxxxxxxx>
Tested-by: Meelis Roos <mroos@xxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Acked-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@xxxxxxxxxxxxx
Link: https://lkml.org/lkml/2018/12/4/206
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[bwh: Backported to 4.9: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a69cfa33f986..a77737a979c8 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -221,9 +221,6 @@ ifdef CONFIG_RETPOLINE
     RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
 
     RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
-    ifeq ($(RETPOLINE_CFLAGS),)
-      $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-    endif
     KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -240,6 +237,13 @@ archscripts: scripts_basic
 ifeq ($(CONFIG_KEXEC_FILE),y)
 	$(Q)$(MAKE) $(build)=arch/x86/purgatory arch/x86/purgatory/kexec-purgatory.c
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+	@echo "You are building kernel with non-retpoline compiler." >&2
+	@echo "Please update your compiler." >&2
+	@false
+endif
+endif
 
 ###
 # Kernel objects
From 7e95e29eb541a62d50df01c8c52f3d75d13a6bec Mon Sep 17 00:00:00 2001
From: WANG Chao <chao.wang@xxxxxxxxx>
Date: Tue, 11 Dec 2018 00:37:25 +0800
Subject: [PATCH 2/2] x86, modpost: Replace last remnants of RETPOLINE with
 CONFIG_RETPOLINE

commit e4f358916d528d479c3c12bd2fd03f2d5a576380 upstream.

Commit

  4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")

replaced the RETPOLINE define with CONFIG_RETPOLINE checks. Remove the
remaining pieces.

 [ bp: Massage commit message. ]

Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Signed-off-by: WANG Chao <chao.wang@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Reviewed-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: linux-kbuild@xxxxxxxxxxxxxxx
Cc: srinivas.eeda@xxxxxxxxxx
Cc: stable <stable@xxxxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20181210163725.95977-1-chao.wang@xxxxxxxxx
[bwh: Backported to 4.9: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c   | 2 +-
 include/linux/compiler-gcc.h | 2 +-
 include/linux/module.h       | 2 +-
 scripts/mod/modpost.c        | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 20b330902e54..94aa0206b1f9 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -586,7 +586,7 @@ static enum spectre_v2_user_mitigation spectre_v2_user_stibp __ro_after_init =
 static enum spectre_v2_user_mitigation spectre_v2_user_ibpb __ro_after_init =
 	SPECTRE_V2_USER_NONE;
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 static bool spectre_v2_bad_module;
 
 bool retpoline_module_ok(bool has_retpoline)
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index d830eddacdc6..1c1ca4168516 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -107,7 +107,7 @@
 #define __weak		__attribute__((weak))
 #define __alias(symbol)	__attribute__((alias(#symbol)))
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 #define __noretpoline __attribute__((indirect_branch("keep")))
 #endif
 
diff --git a/include/linux/module.h b/include/linux/module.h
index 99f330ae13da..be4a3a9fd89c 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -791,7 +791,7 @@ static inline void module_bug_finalize(const Elf_Ehdr *hdr,
 static inline void module_bug_cleanup(struct module *mod) {}
 #endif	/* CONFIG_GENERIC_BUG */
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 extern bool retpoline_module_ok(bool has_retpoline);
 #else
 static inline bool retpoline_module_ok(bool has_retpoline)
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 9abcdf2e8dfe..62b0552b7b71 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2147,7 +2147,7 @@ static void add_intree_flag(struct buffer *b, int is_intree)
 /* Cannot check for assembler */
 static void add_retpoline(struct buffer *b)
 {
-	buf_printf(b, "\n#ifdef RETPOLINE\n");
+	buf_printf(b, "\n#ifdef CONFIG_RETPOLINE\n");
 	buf_printf(b, "MODULE_INFO(retpoline, \"Y\");\n");
 	buf_printf(b, "#endif\n");
 }

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