[PATCH v2] hardening: Enable KCFI and some other options

[Kees Cook]

Add some stuff that got missed along the way:

- CONFIG_UNWIND_PATCH_PAC_INTO_SCS=y so SCS vs PAC is hardware
  selectable.

- CONFIG_X86_KERNEL_IBT=y while a default, just be sure.

- CONFIG_CFI_CLANG=y globally. (And disable FINEIBT since
  it isn't as secure as straight KCFI.)

- CONFIG_PAGE_TABLE_CHECK=y for userspace mapping sanity.

Reviewed-by: Nathan Chancellor <nathan at kernel.org>
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 v2: move CONFIG_CFI_CLANG=y to global config
 v1: https://lore.kernel.org/all/20240426222940.work.884-kees@kernel.org/
---
 arch/arm64/configs/hardening.config | 1 +
 arch/x86/configs/hardening.config   | 6 ++++++
 kernel/configs/hardening.config     | 8 ++++++++
 3 files changed, 15 insertions(+)

diff --git a/arch/arm64/configs/hardening.config b/arch/arm64/configs/hardening.config
index b0e795208998..24179722927e 100644
--- a/arch/arm64/configs/hardening.config
+++ b/arch/arm64/configs/hardening.config
@@ -5,6 +5,7 @@ CONFIG_ARM64_SW_TTBR0_PAN=y
 
 # Software Shadow Stack or PAC
 CONFIG_SHADOW_CALL_STACK=y
+CONFIG_UNWIND_PATCH_PAC_INTO_SCS=y
 
 # Pointer authentication (ARMv8.3 and later). If hardware actually supports
 # it, one can turn off CONFIG_STACKPROTECTOR_STRONG with this enabled.
diff --git a/arch/x86/configs/hardening.config b/arch/x86/configs/hardening.config
index 7b497f3b7bc3..bf3d31618e12 100644
--- a/arch/x86/configs/hardening.config
+++ b/arch/x86/configs/hardening.config
@@ -10,5 +10,11 @@ CONFIG_INTEL_IOMMU_DEFAULT_ON=y
 CONFIG_INTEL_IOMMU_SVM=y
 CONFIG_AMD_IOMMU=y
 
+# Enforce CET Indirect Branch Tracking in the kernel.
+CONFIG_X86_KERNEL_IBT=y
+
 # Enable CET Shadow Stack for userspace.
 CONFIG_X86_USER_SHADOW_STACK=y
+
+# When CONFIG_CFI_CLANG is enabled, disable weaker FINEIBT landing pads.
+# CONFIG_FINEIBT is not set
diff --git a/kernel/configs/hardening.config b/kernel/configs/hardening.config
index 7a5bbfc024b7..47e6564129c3 100644
--- a/kernel/configs/hardening.config
+++ b/kernel/configs/hardening.config
@@ -23,6 +23,10 @@ CONFIG_SLAB_FREELIST_HARDENED=y
 CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
 CONFIG_RANDOM_KMALLOC_CACHES=y
 
+# Sanity check userspace page table mappings.
+CONFIG_PAGE_TABLE_CHECK=y
+CONFIG_PAGE_TABLE_CHECK_ENFORCED=y
+
 # Randomize kernel stack offset on syscall entry.
 CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y
 
@@ -81,6 +85,10 @@ CONFIG_SECCOMP_FILTER=y
 # Provides some protections against SYN flooding.
 CONFIG_SYN_COOKIES=y
 
+# Enable Kernel Control Flow Integrity (currently Clang only).
+CONFIG_CFI_CLANG=y
+# CONFIG_CFI_PERMISSIVE is not set
+
 # Attack surface reduction: do not autoload TTY line disciplines.
 # CONFIG_LDISC_AUTOLOAD is not set
 
-- 
2.34.1