[PATCH v15 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack

Yu-cheng Yu
2020-11-10T16:22:55Z

Shadow Stack provides protection against function return address
corruption. It is active when the processor supports it, the kernel has
CONFIG_X86_SHADOW_STACK_USER, 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>
---
arch/x86/Kconfig | 33 +++++++++++++++++++++++++++
scripts/as-x86_64-has-shadow-stack.sh | 4 ++++
2 files changed, 37 insertions(+)
create mode 100755 scripts/as-x86_64-has-shadow-stack.sh

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f6946b81f74a..a51d2a3de166 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1930,6 +1930,39 @@ config X86_INTEL_TSX_MODE_AUTO
side channel attacks- equals the tsx=auto command line parameter.
endchoice

+config AS_HAS_SHADOW_STACK
+ def_bool $(success,$(srctree)/scripts/as-x86_64-has-shadow-stack.sh $(CC))
+ help
+ Test the assembler for shadow stack instructions.
+
+config X86_CET
+ def_bool n
+
+config ARCH_HAS_SHADOW_STACK
+ def_bool n
+
+config X86_SHADOW_STACK_USER
+ prompt "Intel Shadow Stacks for user-mode"
+ def_bool n
+ depends on CPU_SUP_INTEL && X86_64
+ depends on AS_HAS_SHADOW_STACK
+ select ARCH_USES_HIGH_VMA_FLAGS
+ select X86_CET
+ select ARCH_HAS_SHADOW_STACK
+ help
+ Shadow Stacks provides protection against program stack
+ corruption. It's a hardware feature. This only matters
+ if you have the right hardware. It's a security hardening
+ feature and apps must be enabled to use it. You get no
+ protection "for free" on old userspace. The hardware can
+ support user and kernel, but this option is for user space
+ only.
+ Support for this feature is only known to be present on
+ processors released in 2020 or later. CET features are also
+ known to increase kernel text size by 3.7 KB.
+
+ If unsure, say N.
+
config EFI
bool "EFI runtime service support"
depends on ACPI
diff --git a/scripts/as-x86_64-has-shadow-stack.sh b/scripts/as-x86_64-has-shadow-stack.sh
new file mode 100755
index 000000000000..fac1d363a1b8
--- /dev/null
+++ b/scripts/as-x86_64-has-shadow-stack.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+echo "wrussq %rax, (%rbx)" | $* -x assembler -c -
--
2.21.0