linux-kernel - [PATCH 14/15] x86: Make software tag-based kasan available

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Message-ID: <794a931acfb8e73e28c02932ef08bed9254f164e.1738686764.git.maciej.wieczor-retman@intel.com>
Date: Tue,  4 Feb 2025 18:33:55 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
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Subject: [PATCH 14/15] x86: Make software tag-based kasan available

Make CONFIG_KASAN_SW_TAGS available for x86 machines if they have
ADDRESS_MASKING enabled (LAM) as that works similarly to Top-Byte Ignore
(TBI) that allows the software tag-based mode on arm64 platform.

Set scale macro based on KASAN mode: in software tag-based mode 32 bytes
of memory map to one shadow byte and 16 in generic mode.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
---
 arch/x86/Kconfig                | 8 ++++++++
 arch/x86/boot/compressed/misc.h | 2 ++
 arch/x86/include/asm/kasan.h    | 2 +-
 arch/x86/kernel/setup.c         | 2 ++
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index dfec7bc692d4..afbcf27ad278 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -36,6 +36,7 @@ config X86_64
 	select ARCH_HAS_ELFCORE_COMPAT
 	select ZONE_DMA32
 	select EXECMEM if DYNAMIC_FTRACE
+	select ARCH_HAS_KASAN_SW_TAGS_DENSE
 
 config FORCE_DYNAMIC_FTRACE
 	def_bool y
@@ -190,6 +191,7 @@ config X86
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN			if X86_64
 	select HAVE_ARCH_KASAN_VMALLOC		if X86_64
+	select HAVE_ARCH_KASAN_SW_TAGS		if ADDRESS_MASKING
 	select HAVE_ARCH_KFENCE
 	select HAVE_ARCH_KMSAN			if X86_64
 	select HAVE_ARCH_KGDB
@@ -394,6 +396,12 @@ config KASAN_SHADOW_OFFSET
 	hex
 	default 0xdffffc0000000000 if KASAN_GENERIC
 
+config KASAN_SHADOW_SCALE_SHIFT
+	int
+	default 5 if KASAN_SW_TAGS_DENSE
+	default 4 if KASAN_SW_TAGS
+	default 3
+
 config HAVE_INTEL_TXT
 	def_bool y
 	depends on INTEL_IOMMU && ACPI
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index dd8d1a85f671..397a70558ffa 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -13,6 +13,8 @@
 #undef CONFIG_PARAVIRT_SPINLOCKS
 #undef CONFIG_KASAN
 #undef CONFIG_KASAN_GENERIC
+#undef CONFIG_KASAN_SW_TAGS
+#undef CONFIG_KASAN_SW_TAGS_DENSE
 
 #define __NO_FORTIFY
 
diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index 79151356d5f2..99ff4ae83bf7 100644
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -6,7 +6,7 @@
 #include <linux/kasan-tags.h>
 #include <linux/types.h>
 
-#define KASAN_SHADOW_SCALE_SHIFT 3
+#define KASAN_SHADOW_SCALE_SHIFT CONFIG_KASAN_SHADOW_SCALE_SHIFT
 
 /*
  * Compiler uses shadow offset assuming that addresses start
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f1fea506e20f..c300274e205a 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1121,6 +1121,8 @@ void __init setup_arch(char **cmdline_p)
 
 	kasan_init();
 
+	kasan_init_sw_tags();
+
 	/*
 	 * Sync back kernel address range.
 	 *
-- 
2.47.1