[PATCH v10 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack

Yu-cheng Yu
2020-04-29T22:10:33Z

Shadow Stack provides protection against function return address
corruption. It is active when the processor supports it, the kernel has
CONFIG_X86_INTEL_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>
---
v10:
- Change SHSTK to shadow stack in the help text.
- Change build-time check to config-time check.
- Change ARCH_HAS_SHSTK to ARCH_HAS_SHADOW_STACK.

arch/x86/Kconfig | 30 +++++++++++++++++++++++++++
scripts/as-x86_64-has-shadow-stack.sh | 4 ++++
2 files changed, 34 insertions(+)
create mode 100755 scripts/as-x86_64-has-shadow-stack.sh

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1197b5596d5a..c98f82fffe85 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1947,6 +1947,36 @@ 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_INTEL_CET
+ def_bool n
+
+config ARCH_HAS_SHADOW_STACK
+ def_bool n
+
+config X86_INTEL_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_INTEL_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.
+
+ If unsure, say y.
+
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