x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support

Since retpoline capable compilers are widely available, make
CONFIG_RETPOLINE hard depend on the compiler capability.

Break the build when CONFIG_RETPOLINE is enabled and the compiler does not
support it. Emit an error message in that case:

 "arch/x86/Makefile:226: *** You are building kernel with non-retpoline
  compiler, please update your compiler..  Stop."

[dwmw: Fail the build with non-retpoline compiler]

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Borislav Petkov <bp@suse.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: H. Peter Anvin <hpa@zytor.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>
Cc: <srinivas.eeda@oracle.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/cca0cb20-f9e2-4094-840b-fb0f8810cd34@default
(cherry picked from commit 4cd24de3a0980bf3100c9dcb08ef65ca7c31af48)

Orabug: 29211617

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/Kconfig
	arch/x86/include/asm/nospec-branch.h
Minor differences between UEK and upstream.
	arch/x86/Makefile
Need to add line defining RETPOLINE_CFLAGS.
	arch/x86/kernel/cpu/bugs.c
UEK4 has the corresponding code in bugs_64.c
	scripts/Makefile.build
Commit e699314 (objtool: Add retpoline validation) has not
been ported to UEK4, nothing to change.

Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e73c64fec23194298b08523c6b453380250b5011..40b60ecf8fe5a56612089f8c8d2587592b0df1cc 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -389,10 +389,6 @@ 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.
-
 if X86_32
 config X86_EXTENDED_PLATFORM
        bool "Support for extended (non-PC) x86 platforms"

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a6186d4cef23ff5b4ee9c5e19b592f470d2881a7..dfc305b91e2a45226155eb7c2b5e5455c1a5abb9 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -174,9 +174,10 @@ KBUILD_AFLAGS += $(mflags-y)
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
     RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
-    ifneq ($(RETPOLINE_CFLAGS),)
-        KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
+    ifeq ($(RETPOLINE_CFLAGS),)
+        $(error You are building kernel with non-retpoline compiler, please update your compiler.)
     endif
+    KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
 archscripts: scripts_basic

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index ccfd20a9ef190de6fc17332c41fdcf9c67782e90..b8bd9da307fb59cbedad34f78d3db6ed789c563d 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -131,11 +131,12 @@
 
 #else /* __ASSEMBLY__ */
 
-#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                                           \
        "901: .byte " __stringify(STATIC_KEY_INIT_NOP) "\n"     \
@@ -151,7 +152,7 @@
 
 # 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
@@ -179,6 +180,7 @@
        "905:"
 
 # 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_64.c b/arch/x86/kernel/cpu/bugs_64.c
index f6f9c459a5aa179a81a8f02d786f9e6c6a351862..5dd4b258dcc45841e392f50496784ede55fc94af 100644 (file)
--- a/arch/x86/kernel/cpu/bugs_64.c
+++ b/arch/x86/kernel/cpu/bugs_64.c
@@ -436,7 +436,7 @@ void find_retpoline_alternative(void)
 
 static inline bool retp_compiler(void)
 {
-       return __is_defined(RETPOLINE);
+       return __is_defined(CONFIG_RETPOLINE);
 }
 
 bool retpoline_enabled(void)