Merge tag 'x86_shstk_for_6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 shadow stack support from Dave Hansen:
 "This is the long awaited x86 shadow stack support, part of Intel's
  Control-flow Enforcement Technology (CET).

  CET consists of two related security features: shadow stacks and
  indirect branch tracking. This series implements just the shadow stack
  part of this feature, and just for userspace.

  The main use case for shadow stack is providing protection against
  return oriented programming attacks. It works by maintaining a
  secondary (shadow) stack using a special memory type that has
  protections against modification. When executing a CALL instruction,
  the processor pushes the return address to both the normal stack and
  to the special permission shadow stack. Upon RET, the processor pops
  the shadow stack copy and compares it to the normal stack copy.

  For more information, refer to the links below for the earlier
  versions of this patch set"

Link: https://lore.kernel.org/lkml/20220130211838.8382-1-rick.p.edgecombe@intel.com/
Link: https://lore.kernel.org/lkml/20230613001108.3040476-1-rick.p.edgecombe@intel.com/

* tag 'x86_shstk_for_6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (47 commits)
  x86/shstk: Change order of __user in type
  x86/ibt: Convert IBT selftest to asm
  x86/shstk: Don't retry vm_munmap() on -EINTR
  x86/kbuild: Fix Documentation/ reference
  x86/shstk: Move arch detail comment out of core mm
  x86/shstk: Add ARCH_SHSTK_STATUS
  x86/shstk: Add ARCH_SHSTK_UNLOCK
  x86: Add PTRACE interface for shadow stack
  selftests/x86: Add shadow stack test
  x86/cpufeatures: Enable CET CR4 bit for shadow stack
  x86/shstk: Wire in shadow stack interface
  x86: Expose thread features in /proc/$PID/status
  x86/shstk: Support WRSS for userspace
  x86/shstk: Introduce map_shadow_stack syscall
  x86/shstk: Check that signal frame is shadow stack mem
  x86/shstk: Check that SSP is aligned on sigreturn
  x86/shstk: Handle signals for shadow stack
  x86/shstk: Introduce routines modifying shstk
  x86/shstk: Handle thread shadow stack
  x86/shstk: Add user-mode shadow stack support
  ...

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bd9a1804cf72..982b777eadc7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1815,6 +1815,11 @@ 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
@@ -1822,6 +1827,7 @@ 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
@@ -1915,6 +1921,24 @@ 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/arch/x86/shstk.rst for more information.
+
+	  If unsure, say N.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI