Since retpoline capable compilers are widely available, make CONFIG_RETPOLINE hard depend on it. This is achieved by breaking the build early and showing an error like below:
"arch/x86/Makefile:226: *** You are building kernel with non-retpoline compiler, please update your compiler.. Stop." [pet...@infradead.org: initial suggestion] Link: https://lore.kernel.org/lkml/caeb3213f13e57191e362ca04f2892cfa2ccda65.ca...@infradead.org [d...@amazon.co.uk: fail the build with non-retpoline compiler] Link: https://lore.kernel.org/lkml/alpine.deb.2.21.1811011317400.1...@nanos.tec.linutronix.de Signed-off-by: Zhenzhong Duan <zhenzhong.d...@oracle.com> Suggested-by: Peter Zijlstra <pet...@infradead.org> Cc: David Woodhouse <d...@amazon.co.uk> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Borislav Petkov <b...@suse.de> Cc: Daniel Borkmann <dan...@iogearbox.net> Cc: H. Peter Anvin <h...@zytor.com> Cc: Ingo Molnar <mi...@redhat.com> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> Cc: Andy Lutomirski <l...@kernel.org> Cc: Masahiro Yamada <yamada.masah...@socionext.com> Cc: Michal Marek <michal.l...@markovi.net> --- arch/x86/Kconfig | 4 ---- arch/x86/Makefile | 5 +++-- arch/x86/include/asm/nospec-branch.h | 10 ++++++---- arch/x86/kernel/cpu/bugs.c | 2 +- scripts/Makefile.build | 2 -- 5 files changed, 10 insertions(+), 13 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index c51c989..fcb7f37 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -443,10 +443,6 @@ 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. - config INTEL_RDT bool "Intel Resource Director Technology support" depends on X86 && CPU_SUP_INTEL diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 5b562e4..6d94fe8 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -222,9 +222,10 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables # Avoid indirect branches in kernel to deal with Spectre ifdef CONFIG_RETPOLINE -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 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/scripts/Makefile.build b/scripts/Makefile.build index a8e7ba9..6a6be9f 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -236,10 +236,8 @@ ifdef CONFIG_GCOV_KERNEL objtool_args += --no-unreachable endif ifdef CONFIG_RETPOLINE -ifneq ($(RETPOLINE_CFLAGS),) objtool_args += --retpoline endif -endif ifdef CONFIG_MODVERSIONS -- 1.8.3.1
