[PATCH v5 19/19] x86: Make software tag-based kasan available

[Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>]

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 16 bytes
of memory map to one shadow byte and 8 in generic mode.

Disable CONFIG_KASAN_INLINE and CONFIG_KASAN_STACK when
CONFIG_KASAN_SW_TAGS is enabled on x86 until the appropriate compiler
support is available.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v4:
- Add x86 specific kasan_mem_to_shadow().
- Revert x86 to the older unsigned KASAN_SHADOW_OFFSET. Do the same to
  KASAN_SHADOW_START/END.
- Modify scripts/gdb/linux/kasan.py to keep x86 using unsigned offset.
- Disable inline and stack support when software tags are enabled on
  x86.

Changelog v3:
- Remove runtime_const from previous patch and merge the rest here.
- Move scale shift definition back to header file.
- Add new kasan offset for software tag based mode.
- Fix patch message typo 32 -> 16, and 16 -> 8.
- Update lib/Kconfig.kasan with x86 now having software tag-based
  support.

Changelog v2:
- Remove KASAN dense code.

 Documentation/arch/x86/x86_64/mm.rst | 6 ++++--
 arch/x86/Kconfig                     | 4 +++-
 arch/x86/boot/compressed/misc.h      | 1 +
 arch/x86/include/asm/kasan.h         | 1 +
 arch/x86/kernel/setup.c              | 2 ++
 lib/Kconfig.kasan                    | 3 ++-
 scripts/gdb/linux/kasan.py           | 4 ++--
 7 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/Documentation/arch/x86/x86_64/mm.rst b/Documentation/arch/x86/x86_64/mm.rst
index a6cf05d51bd8..ccbdbb4cda36 100644
--- a/Documentation/arch/x86/x86_64/mm.rst
+++ b/Documentation/arch/x86/x86_64/mm.rst
@@ -60,7 +60,8 @@ Complete virtual memory map with 4-level page tables
    ffffe90000000000 |  -23    TB | ffffe9ffffffffff |    1 TB | ... unused hole
    ffffea0000000000 |  -22    TB | ffffeaffffffffff |    1 TB | virtual memory map (vmemmap_base)
    ffffeb0000000000 |  -21    TB | ffffebffffffffff |    1 TB | ... unused hole
-   ffffec0000000000 |  -20    TB | fffffbffffffffff |   16 TB | KASAN shadow memory
+   ffffec0000000000 |  -20    TB | fffffbffffffffff |   16 TB | KASAN shadow memory (generic mode)
+   fffff40000000000 |   -8    TB | fffffbffffffffff |    8 TB | KASAN shadow memory (software tag-based mode)
   __________________|____________|__________________|_________|____________________________________________________________
                                                               |
                                                               | Identical layout to the 56-bit one from here on:
@@ -130,7 +131,8 @@ Complete virtual memory map with 5-level page tables
    ffd2000000000000 |  -11.5  PB | ffd3ffffffffffff |  0.5 PB | ... unused hole
    ffd4000000000000 |  -11    PB | ffd5ffffffffffff |  0.5 PB | virtual memory map (vmemmap_base)
    ffd6000000000000 |  -10.5  PB | ffdeffffffffffff | 2.25 PB | ... unused hole
-   ffdf000000000000 |   -8.25 PB | fffffbffffffffff |   ~8 PB | KASAN shadow memory
+   ffdf000000000000 |   -8.25 PB | fffffbffffffffff |   ~8 PB | KASAN shadow memory (generic mode)
+   ffeffc0000000000 |   -6    PB | fffffbffffffffff |    4 PB | KASAN shadow memory (software tag-based mode)
   __________________|____________|__________________|_________|____________________________________________________________
                                                               |
                                                               | Identical layout to the 47-bit one from here on:
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b8df57ac0f28..f44fec1190b6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -69,6 +69,7 @@ config X86
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_CONFIGURES_CPU_MITIGATIONS
 	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
+	select ARCH_DISABLE_KASAN_INLINE	if X86_64 && KASAN_SW_TAGS
 	select ARCH_ENABLE_HUGEPAGE_MIGRATION if X86_64 && HUGETLB_PAGE && MIGRATION
 	select ARCH_ENABLE_MEMORY_HOTPLUG if X86_64
 	select ARCH_ENABLE_MEMORY_HOTREMOVE if MEMORY_HOTPLUG
@@ -199,6 +200,7 @@ 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
@@ -403,7 +405,7 @@ config AUDIT_ARCH
 
 config KASAN_SHADOW_OFFSET
 	hex
-	depends on KASAN
+	default 0xeffffc0000000000 if KASAN_SW_TAGS
 	default 0xdffffc0000000000
 
 config HAVE_INTEL_TXT
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index db1048621ea2..ded92b439ada 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 f3e34a9754d2..385f4e9daab3 100644
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -7,6 +7,7 @@
 #include <linux/types.h>
 #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
 #ifdef CONFIG_KASAN_SW_TAGS
+#define KASAN_SHADOW_SCALE_SHIFT 4
 
 /*
  * LLVM ABI for reporting tag mismatches in inline KASAN mode.
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 1b2edd07a3e1..5b819f84f6db 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1207,6 +1207,8 @@ void __init setup_arch(char **cmdline_p)
 
 	kasan_init();
 
+	kasan_init_sw_tags();
+
 	/*
 	 * Sync back kernel address range.
 	 *
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f82889a830fa..9ddbc6aeb5d5 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -100,7 +100,8 @@ config KASAN_SW_TAGS
 
 	  Requires GCC 11+ or Clang.
 
-	  Supported only on arm64 CPUs and relies on Top Byte Ignore.
+	  Supported on arm64 CPUs that support Top Byte Ignore and on x86 CPUs
+	  that support Linear Address Masking.
 
 	  Consumes about 1/16th of available memory at kernel start and
 	  add an overhead of ~20% for dynamic allocations.
diff --git a/scripts/gdb/linux/kasan.py b/scripts/gdb/linux/kasan.py
index fca39968d308..4b86202b155f 100644
--- a/scripts/gdb/linux/kasan.py
+++ b/scripts/gdb/linux/kasan.py
@@ -7,7 +7,7 @@
 #
 
 import gdb
-from linux import constants, mm
+from linux import constants, utils, mm
 from ctypes import c_int64 as s64
 
 def help():
@@ -40,7 +40,7 @@ class KasanMemToShadow(gdb.Command):
         else:
             help()
     def kasan_mem_to_shadow(self, addr):
-        if constants.CONFIG_KASAN_SW_TAGS:
+        if constants.CONFIG_KASAN_SW_TAGS and not utils.is_target_arch('x86'):
             addr = s64(addr)
         return (addr >> self.p_ops.KASAN_SHADOW_SCALE_SHIFT) + self.p_ops.KASAN_SHADOW_OFFSET
 
-- 
2.50.1