[PATCH 02/35] x86/cet/shstk: Add Kconfig option for Shadow Stack

Rick Edgecombe
2022-01-30T21:21:52Z

From: Yu-cheng Yu <yu-cheng.yu@intel.com>

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@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Kees Cook <keescook@chromium.org>
---

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 | 22 ++++++++++++++++++++++
arch/x86/Kconfig.assembler | 5 +++++
2 files changed, 27 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ebe8fc76949a..b9efa0fd906d 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
@@ -1940,6 +1941,27 @@ config X86_SGX

If unsure, say N.

+config ARCH_HAS_SHADOW_STACK
+ def_bool n
+
+config X86_SHADOW_STACK
+ prompt "Intel Shadow Stack"
+ def_bool n
+ depends on AS_WRUSS
+ depends on ARCH_HAS_SHADOW_STACK
+ select ARCH_USES_HIGH_VMA_FLAGS
+ help
+ Shadow Stack protection is a hardware feature that detects function
+ return address corruption. This helps 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
--
2.17.1