On 11/27/2020 9:10 AM, Borislav Petkov wrote:
On Tue, Nov 10, 2020 at 08:21:50AM -0800, Yu-cheng Yu wrote:
+config X86_CET
+ def_bool n
+
+config ARCH_HAS_SHADOW_STACK
+ def_bool n
+
+config X86_SHADOW_STACK_USER
Is X86_SHADOW_STACK_KERNEL coming too?
Regardless, you can add it when it comes and you can use only X86_CET
for now and drop this one and simplify this pile of Kconfig symbols.
We have X86_BRANCH_TRACKING_USER too. My thought was, X86_CET means any
of kernel/user shadow stack/ibt.
+ 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.
This help text needs some rewriting. You can find an inspiration about
more adequate style in that same Kconfig file.
I will work on it.
+
+ 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> /dev/null
otherwise you get
{standard input}: Assembler messages:
{standard input}:1: Error: no such instruction: `wrussq %rax,(%rbx)
on non-enlightened toolchains during build.
Yes, I will fix this in the next revision.
Yu-cheng
Thx.
