[PATCH 01/19] x86/cet/shstk: Add Kconfig option for Shadow Stack

[Yang Weijiang]

From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

Shadow Stack provides protection against function return address
corruption. It is active when the processor supports it, the kernel has
CONFIG_X86_SHADOW_STACK 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@xxxxxxxxx>
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>

---
v2:
 - Remove already wrong kernel size increase info (tlgx)
 - Change prompt to remove "Intel" (tglx)
 - Update line about what CPUs are supported (Dave)

Yu-cheng v25:
 - Remove X86_CET and use X86_SHADOW_STACK directly.

Yu-cheng v24:
 - Update for the splitting X86_CET to X86_SHADOW_STACK and X86_IBT.

 arch/x86/Kconfig           | 17 +++++++++++++++++
 arch/x86/Kconfig.assembler |  1 +
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9783ebc4e021..79c6b0490350 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -26,6 +26,7 @@ config X86_64
 	depends on 64BIT
 	# Options that are inherently 64-bit kernel only:
 	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_HAS_SHADOW_STACK
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select HAVE_ARCH_SOFT_DIRTY
@@ -1969,6 +1970,22 @@ config X86_SGX
 
 	  If unsure, say N.
 
+config ARCH_HAS_SHADOW_STACK
+	def_bool n
+
+config X86_SHADOW_STACK
+	prompt "X86 Shadow Stack"
+	def_bool n
+	depends on ARCH_HAS_SHADOW_STACK
+	help
+	  Shadow Stack protection is a hardware feature that detects function
+	  return address corruption. Today the kernel's support is limited to
+	  virtualizing it in KVM guests.
+
+	  CPUs supporting shadow stacks were first released in 2020.
+
+	  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..41428391e475 100644
--- a/arch/x86/Kconfig.assembler
+++ b/arch/x86/Kconfig.assembler
@@ -19,3 +19,4 @@ config AS_TPAUSE
 	def_bool $(as-instr,tpause %ecx)
 	help
 	  Supported by binutils >= 2.31.1 and LLVM integrated assembler >= V7
+
-- 
2.27.0