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Date:   Thu, 11 Feb 2021 21:14:58 -0800
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Subject: [PATCH] ARM: Implement Clang's SLS mitigation
From:   Jian Cai <jiancai@google.com>
Cc:     ndesaulniers@google.com, manojgupta@google.com, llozano@google.com,
        clang-built-linux@googlegroups.com, Jian Cai <jiancai@google.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Daniel Palmer <daniel@0x0f.com>,
        "=?UTF-8?q?Andreas=20F=C3=A4rber?=" <afaerber@suse.de>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org
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Precedence: bulk

This patch adds a config CONFIG_HARDEN_SLS_ALL that can be used to turn
on -mharden-sls=all, which mitigates the straight-line speculation
vulnerability, or more commonly known as Spectre, Meldown.

Notice -mharden-sls= has other options as below, and this config turns
on the strongest option.

all: enable all mitigations against Straight Line Speculation that are implemented.
none: disable all mitigations against Straight Line Speculation.
retbr: enable the mitigation against Straight Line Speculation for RET and BR instructions.
blr: enable the mitigation against Straight Line Speculation for BLR instructions.

Link: https://reviews.llvm.org/D93221
Link: https://reviews.llvm.org/D81404
Link: https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
Link: https://crbug.com/1171521

Suggested-by: Manoj Gupta <manojgupta@google.com>
Signed-off-by: Jian Cai <jiancai@google.com>
---
 arch/arm/Makefile          |  4 ++++
 arch/arm64/Makefile        |  5 +++++
 security/Kconfig.hardening | 11 +++++++++++
 3 files changed, 20 insertions(+)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 4aaec9599e8a..11d89ef32da9 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -48,6 +48,10 @@ CHECKFLAGS	+= -D__ARMEL__
 KBUILD_LDFLAGS	+= -EL
 endif
 
+ifeq ($(CONFIG_HARDEN_SLS_ALL), y)
+KBUILD_CFLAGS  += -mharden-sls=all
+endif
+
 #
 # The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
 # later may result in code being generated that handles signed short and signed
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 90309208bb28..8fd0ccd87eca 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -34,6 +34,11 @@ $(warning LSE atomics not supported by binutils)
   endif
 endif
 
+ifeq ($(CONFIG_HARDEN_SLS_ALL), y)
+KBUILD_CFLAGS  += -mharden-sls=all
+endif
+
+
 cc_has_k_constraint := $(call try-run,echo				\
 	'int main(void) {						\
 		asm volatile("and w0, w0, %w0" :: "K" (4294967295));	\
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index 269967c4fc1b..d83c406c81a3 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -121,6 +121,17 @@ choice
 
 endchoice
 
+
+config CC_HAS_HARDEN_SLS_ALL
+	def_bool $(cc-option,-mharden-sls=all)
+
+	config HARDEN_SLS_ALL
+               bool "enable SLS vulnerability hardening"
+               depends on CC_HAS_HARDEN_SLS_ALL
+               help
+                 Enables straight-line speculation vulnerability hardening
+		 at highest level.
+
 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 	bool "Report forcefully initialized variables"
 	depends on GCC_PLUGIN_STRUCTLEAK
-- 
2.30.0.478.g8a0d178c01-goog