linux-kernel - [PATCH v2 14/14] x86: Make software tag-based kasan available

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Message-ID: <d266338a0eae1f673802e41d7230c4c92c3532b3.1739866028.git.maciej.wieczor-retman@intel.com>
Date: Tue, 18 Feb 2025 09:15:30 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
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Subject: [PATCH v2 14/14] 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>
---
Changelog v2:
- Remove KASAN dense code.

 arch/x86/Kconfig                | 6 ++++++
 arch/x86/boot/compressed/misc.h | 1 +
 arch/x86/include/asm/kasan.h    | 2 +-
 arch/x86/kernel/setup.c         | 2 ++
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f4ef64bf824a..dc48eb5b664f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -195,6 +195,7 @@ 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
@@ -402,6 +403,11 @@ config KASAN_SHADOW_OFFSET
 	hex
 	default 0xdffffc0000000000 if KASAN_GENERIC
 
+config KASAN_SHADOW_SCALE_SHIFT
+	int
+	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..f6a87e9ad200 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -13,6 +13,7 @@
 #undef CONFIG_PARAVIRT_SPINLOCKS
 #undef CONFIG_KASAN
 #undef CONFIG_KASAN_GENERIC
+#undef CONFIG_KASAN_SW_TAGS
 
 #define __NO_FORTIFY
 
diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index 4bfd3641af84..cfc31e4a2f70 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 cebee310e200..768990c573ea 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1124,6 +1124,8 @@ void __init setup_arch(char **cmdline_p)
 
 	kasan_init();
 
+	kasan_init_sw_tags();
+
 	/*
 	 * Sync back kernel address range.
 	 *
-- 
2.47.1