[PATCH 25/35] kasan: introduce CONFIG_KASAN_HW_TAGS

[Andrey Konovalov]

This patch adds a configuration option for a new KASAN mode called
hardware tag-based KASAN. This mode uses the memory tagging approach
like the software tag-based mode, but relies on arm64 Memory Tagging
Extension feature for tag management and access checking.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
---
 lib/Kconfig.kasan | 46 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index e500c18cbe79..0d4160ce5ee8 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -6,7 +6,10 @@ config HAVE_ARCH_KASAN
 config HAVE_ARCH_KASAN_SW_TAGS
 	bool
 
-config	HAVE_ARCH_KASAN_VMALLOC
+config HAVE_ARCH_KASAN_HW_TAGS
+	bool
+
+config HAVE_ARCH_KASAN_VMALLOC
 	bool
 
 config CC_HAS_KASAN_GENERIC
@@ -20,10 +23,11 @@ config CC_HAS_WORKING_NOSANITIZE_ADDRESS
 
 menuconfig KASAN
 	bool "KASAN: runtime memory debugger"
-	depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
-		   (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
+	depends on (((HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
+		     (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
+		    CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
+		   HAVE_ARCH_KASAN_HW_TAGS
 	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
-	depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
 	select SLUB_DEBUG if SLUB
 	select CONSTRUCTORS
 	select STACKDEPOT
@@ -38,13 +42,18 @@ choice
 	prompt "KASAN mode"
 	default KASAN_GENERIC
 	help
-	  KASAN has two modes: generic KASAN (similar to userspace ASan,
-	  x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
-	  software tag-based KASAN (a version based on software memory
-	  tagging, arm64 only, similar to userspace HWASan, enabled with
-	  CONFIG_KASAN_SW_TAGS).
+	  KASAN has three modes:
+	  1. generic KASAN (similar to userspace ASan,
+	     x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC),
+	  2. software tag-based KASAN (arm64 only, based on software
+	     memory tagging (similar to userspace HWASan), enabled with
+	     CONFIG_KASAN_SW_TAGS), and
+	  3. hardware tag-based KASAN (arm64-only, based hardware
+	     memory tagging (MTE), enabled with CONFIG_KASAN_HW_TAGS).
+
+	  All KASAN modes are strictly debugging features.
 
-	  Both generic and tag-based KASAN are strictly debugging features.
+	  For better error detection enable CONFIG_STACKTRACE.
 
 config KASAN_GENERIC
 	bool "Generic mode"
@@ -61,8 +70,6 @@ config KASAN_GENERIC
 	  and introduces an overhead of ~x1.5 for the rest of the allocations.
 	  The performance slowdown is ~x3.
 
-	  For better error detection enable CONFIG_STACKTRACE.
-
 	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
@@ -83,15 +90,25 @@ config KASAN_SW_TAGS
 	  casting and comparison, as it embeds tags into the top byte of each
 	  pointer.
 
-	  For better error detection enable CONFIG_STACKTRACE.
-
 	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
+config KASAN_HW_TAGS
+	bool "Hardware tag-based mode"
+	depends on HAVE_ARCH_KASAN_HW_TAGS
+	depends on SLUB
+	help
+	  Enables hardware tag-based KASAN mode.
+
+	  This mode requires both Memory Tagging Extension and Top Byte Ignore
+	  support by the CPU and therefore is only supported for modern arm64
+	  CPUs (MTE added in ARMv8.5 ISA).
+
 endchoice
 
 choice
 	prompt "Instrumentation type"
+	depends on KASAN_GENERIC || KASAN_SW_TAGS
 	default KASAN_OUTLINE
 
 config KASAN_OUTLINE
@@ -115,6 +132,7 @@ endchoice
 
 config KASAN_STACK_ENABLE
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
+	depends on KASAN_GENERIC || KASAN_SW_TAGS
 	help
 	  The LLVM stack address sanitizer has a know problem that
 	  causes excessive stack usage in a lot of functions, see
-- 
2.28.0.220.ged08abb693-goog