[PATCH v3 22/39] kasan: introduce CONFIG_KASAN_HW_TAGS

Andrey Konovalov
2020-09-24T22:51:58Z

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@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
Change-Id: I246c2def9fffa6563278db1bddfbe742ca7bdefe
---
lib/Kconfig.kasan | 59 ++++++++++++++++++++++++++++++++---------------
1 file changed, 41 insertions(+), 18 deletions(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index b4cf6c519d71..516d3a24f7d7 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
@@ -20,11 +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
help
@@ -38,17 +41,23 @@ 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 on hardware
+ memory tagging, 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 reports enable CONFIG_STACKTRACE.

config KASAN_GENERIC
bool "Generic mode"
depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
+ select SLUB_DEBUG if SLUB
help
Enables generic KASAN mode.

@@ -61,20 +70,21 @@ 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).

config KASAN_SW_TAGS
bool "Software tag-based mode"
depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
+ select SLUB_DEBUG if SLUB
help
Enables software tag-based KASAN mode.

- This mode requires Top Byte Ignore support by the CPU and therefore
- is only supported for arm64. This mode requires Clang version 7.0.0
- or later.
+ This mode require software memory tagging support in the form of
+ HWASan-like compiler instrumentation.
+
+ Currently this mode is only implemented for arm64 CPUs and relies on
+ Top Byte Ignore. This mode requires Clang version 7.0.0 or later.

This mode consumes about 1/16th of available memory at kernel start
and introduces an overhead of ~20% for the rest of the allocations.
@@ -82,15 +92,27 @@ 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 hardware memory tagging support, and can be used
+ by any architecture that provides it.
+
+ Currently this mode is only implemented for arm64 CPUs starting from
+ ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore.
+
endchoice

choice
prompt "Instrumentation type"
+ depends on KASAN_GENERIC || KASAN_SW_TAGS
default KASAN_OUTLINE

config KASAN_OUTLINE
@@ -114,6 +136,7 @@ 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
--
2.28.0.681.g6f77f65b4e-goog