linux-kernel - [PATCH] hardening: Refresh KCFI options, add some more

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Message-Id: <20240426222940.work.884-kees@kernel.org>
Date: Fri, 26 Apr 2024 15:29:44 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-hardening@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] hardening: Refresh KCFI options, add some more

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 for x86 and arm64. (And disable FINEIBT since
  it isn't as secure as straight KCFI.)

- CONFIG_PAGE_TABLE_CHECK=y for userspace mapping sanity.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86@...nel.org
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Bill Wendling <morbo@...gle.com>
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: linux-hardening@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: llvm@...ts.linux.dev
---
 arch/arm64/configs/hardening.config | 5 +++++
 arch/x86/configs/hardening.config   | 9 +++++++++
 kernel/configs/hardening.config     | 4 ++++
 3 files changed, 18 insertions(+)

diff --git a/arch/arm64/configs/hardening.config b/arch/arm64/configs/hardening.config
index b0e795208998..e8a18fec7a3e 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.
@@ -20,3 +21,7 @@ CONFIG_ARM64_E0PD=y
 
 # Available in ARMv8.7 and later.
 CONFIG_ARM64_EPAN=y
+
+# Enable Kernel Control Flow Integrity (currently Clang only).
+CONFIG_CFI_CLANG=y
+# CONFIG_CFI_PERMISSIVE is not set
diff --git a/arch/x86/configs/hardening.config b/arch/x86/configs/hardening.config
index 7b497f3b7bc3..b47e5f411dd3 100644
--- a/arch/x86/configs/hardening.config
+++ b/arch/x86/configs/hardening.config
@@ -10,5 +10,14 @@ 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 Kernel Control Flow Integrity (currently Clang only), but disable
+# weaker FINEIBT landing pads.
+CONFIG_CFI_CLANG=y
+# CONFIG_CFI_PERMISSIVE is not set
+# CONFIG_FINEIBT is not set
+
 # Enable CET Shadow Stack for userspace.
 CONFIG_X86_USER_SHADOW_STACK=y
diff --git a/kernel/configs/hardening.config b/kernel/configs/hardening.config
index 7a5bbfc024b7..4be0de1f085c 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
 
-- 
2.34.1