[PATCH v23 02/28] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection

Yu-cheng Yu
2021-03-16T15:12:24Z

Shadow Stack provides protection against function return address
corruption. It is active when the processor supports it, the kernel has
CONFIG_X86_CET 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@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
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 2792879d398e..bdfecc17c2d3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -28,6 +28,7 @@ config X86_64
select ARCH_HAS_GIGANTIC_PAGE
select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
select ARCH_USE_CMPXCHG_LOCKREF
+ select ARCH_HAS_SHADOW_STACK
select HAVE_ARCH_SOFT_DIRTY
select MODULES_USE_ELF_RELA
select NEED_DMA_MAP_STATE
@@ -1941,6 +1942,27 @@ config X86_SGX

If unsure, say N.

+config ARCH_HAS_SHADOW_STACK
+ def_bool n
+
+config X86_CET
+ prompt "Intel Control-flow protection for user-mode"
+ def_bool n
+ depends on AS_WRUSS
+ depends on ARCH_HAS_SHADOW_STACK
+ select ARCH_USES_HIGH_VMA_FLAGS
+ help
+ Control-flow protection is a set of hardware features which place
+ additional restrictions on indirect branches. These help
+ mitigate ROP attacks. Applications must be enabled to use it,
+ and old userspace does not get protection "for free".
+ Support for this feature is present on Tiger Lake family of
+ 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