linux-hardening - [PATCH v5 13/15] x86, cpu: Use LTO for cpu.c with CFI

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Date:   Wed, 13 Oct 2021 11:16:56 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v5 13/15] x86, cpu: Use LTO for cpu.c with CFI

Allow LTO to be used for cpu.c when CONFIG_CFI_CLANG is enabled to avoid
indirect call failures. CFI requires Clang >= 13, which doesn't have the
stack protector inlining bug.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
---
 arch/x86/power/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/power/Makefile b/arch/x86/power/Makefile
index 379777572bc9..a0532851fed7 100644
--- a/arch/x86/power/Makefile
+++ b/arch/x86/power/Makefile
@@ -4,9 +4,11 @@
 # itself be stack-protected
 CFLAGS_cpu.o	:= -fno-stack-protector
 
+ifndef CONFIG_CFI_CLANG
 # Clang may incorrectly inline functions with stack protector enabled into
 # __restore_processor_state(): https://bugs.llvm.org/show_bug.cgi?id=47479
 CFLAGS_REMOVE_cpu.o := $(CC_FLAGS_LTO)
+endif
 
 obj-$(CONFIG_PM_SLEEP)		+= cpu.o
 obj-$(CONFIG_HIBERNATION)	+= hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o
-- 
2.33.0.1079.g6e70778dc9-goog