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Date:   Tue, 29 Dec 2020 13:30:29 -0800
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v17 02/26] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection

Shadow Stack provides protection against function return address
corruption.  It is active when the processor supports it, the kernel has
CONFIG_X86_CET_USER enabled, and the application is built for the feature.
This is only implemented for the 64-bit kernel.  When it is enabled, legacy
non-Shadow Stack applications continue to work, but without protection.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/Kconfig           | 22 ++++++++++++++++++++++
 arch/x86/Kconfig.assembler |  5 +++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7b6dd10b162a..72cff400b9ae 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1950,6 +1950,28 @@ config X86_SGX
 
 	  If unsure, say N.
 
+config ARCH_HAS_SHADOW_STACK
+	def_bool n
+
+config X86_CET_USER
+	prompt "Intel Control-flow protection for user-mode"
+	def_bool n
+	depends on CPU_SUP_INTEL && X86_64
+	depends on AS_WRUSS
+	select ARCH_USES_HIGH_VMA_FLAGS
+	select ARCH_HAS_SHADOW_STACK
+	help
+	  Control-flow protection is a hardware security hardening feature
+	  that detects function-return address or jump target changes by
+	  malicious code.  Applications must be enabled to use it, and old
+	  userspace does not get protection "for free".
+	  Support for this feature is present on processors released in
+	  2020 or later.  Enabling this feature increases kernel text size
+	  by 3.7 KB.
+	  See Documentation/x86/intel_cet.rst for more information.
+
+	  If unsure, say N.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
diff --git a/arch/x86/Kconfig.assembler b/arch/x86/Kconfig.assembler
index 26b8c08e2fc4..00c79dd93651 100644
--- a/arch/x86/Kconfig.assembler
+++ b/arch/x86/Kconfig.assembler
@@ -19,3 +19,8 @@ config AS_TPAUSE
 	def_bool $(as-instr,tpause %ecx)
 	help
 	  Supported by binutils >= 2.31.1 and LLVM integrated assembler >= V7
+
+config AS_WRUSS
+	def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
+	help
+	  Supported by binutils >= 2.31 and LLVM integrated assembler
-- 
2.21.0

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