[tip: x86/shstk] x86/shstk: Add Kconfig option for shadow stack

["tip-bot2 for Rick Edgecombe" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/shstk branch of tip:

Commit-ID:     76aced427011fe790520b191186b0fc9b47c841b
Gitweb:        https://git.kernel.org/tip/76aced427011fe790520b191186b0fc9b47c841b
Author:        Rick Edgecombe <rick.p.edgecombe@intel.com>
AuthorDate:    Mon, 12 Jun 2023 17:10:32 -07:00
Committer:     Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Thu, 15 Jun 2023 16:31:00 -07:00

x86/shstk: Add Kconfig option for shadow stack

Shadow stack provides protection for applications 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.

Since there is another feature that utilizes CET (Kernel IBT) that will
share implementation with shadow stacks, create CONFIG_CET to signify
that at least one CET feature is configured.

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-7-rick.p.edgecombe%40intel.com
---
 arch/x86/Kconfig           | 24 ++++++++++++++++++++++++
 arch/x86/Kconfig.assembler |  5 +++++
 2 files changed, 29 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 53bab12..ce460d6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1852,6 +1852,11 @@ config CC_HAS_IBT
 		  (CC_IS_CLANG && CLANG_VERSION >= 140000)) && \
 		  $(as-instr,endbr64)
 
+config X86_CET
+	def_bool n
+	help
+	  CET features configured (Shadow stack or IBT)
+
 config X86_KERNEL_IBT
 	prompt "Indirect Branch Tracking"
 	def_bool y
@@ -1859,6 +1864,7 @@ config X86_KERNEL_IBT
 	# https://github.com/llvm/llvm-project/commit/9d7001eba9c4cb311e03cd8cdc231f9e579f2d0f
 	depends on !LD_IS_LLD || LLD_VERSION >= 140000
 	select OBJTOOL
+	select X86_CET
 	help
 	  Build the kernel with support for Indirect Branch Tracking, a
 	  hardware support course-grain forward-edge Control Flow Integrity
@@ -1952,6 +1958,24 @@ config X86_SGX
 
 	  If unsure, say N.
 
+config X86_USER_SHADOW_STACK
+	bool "X86 userspace shadow stack"
+	depends on AS_WRUSS
+	depends on X86_64
+	select ARCH_USES_HIGH_VMA_FLAGS
+	select X86_CET
+	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".
+
+	  CPUs supporting shadow stacks were first released in 2020.
+
+	  See Documentation/x86/shstk.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 b88f784..8ad41da 100644
--- a/arch/x86/Kconfig.assembler
+++ b/arch/x86/Kconfig.assembler
@@ -24,3 +24,8 @@ config AS_GFNI
 	def_bool $(as-instr,vgf2p8mulb %xmm0$(comma)%xmm1$(comma)%xmm2)
 	help
 	  Supported by binutils >= 2.30 and LLVM integrated assembler
+
+config AS_WRUSS
+	def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
+	help
+	  Supported by binutils >= 2.31 and LLVM integrated assembler