ANDROID: gki_defconfig: enable CONFIG_KASAN_HW_TAGS

Enable in-kernel MTE (Memory Tagging Extension) support via
CONFIG_KASAN_HW_TAGS=y. With this change in-kernel MTE will be
auto-enabled during boot on hardware that supports MTE.

Currently, in-kernel MTE is only supported for slab and page_alloc
allocations. Future changes might include support for vmalloc, stack,
and globals.

By default:

- MTE works in synchronous mode, which means that tag faults are being
  reported at the point of occurence.
- When a tag fault is detected, a report is printed into the kernel log.
  Only the first tag fault gets reported. No panic occurs unless either
  "kasan.fault=panic" or "panic_on_warn" is set via command line.
- A report contains the address and a stack trace of the access.
  There are no alloc/free stack traces for the accessed page or slab
  object (as specified via CONFIG_CMDLINE in this change).

These defaults can be overridden via command line parameters, see
Documentation/dev-tools/kasan.rst for details. In particular, using
the "kasan=off" command line parameter will turn in-kernel MTE off.
Note, that enabling alloc/free stacktraces requires specifying both
"kasan.stacktrace=on" and "stack_depot_disable=off".

On MTE-enabled hardware, a performance impact of ~10% is expected, but
there is no such hardware yet to run benchmarks. A future integration of
in-kernel MTE with init_on_alloc/free might significantly bring down the
perfomance impact.

There is no performance impact when in-kernel MTE is disabled via
command line or when hardware without MTE (pre-ARMv8.5) is in use.
There is still a side-effect of TTBR1 TBI (Top Byte Ignore) getting
enabled with CONFIG_KASAN_HW_TAGS=y.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Bug: 172318110
Change-Id: I2f9bb845ae43292c182532e5e42f43e07b4d0d56

arch/arm64/configs/gki_defconfig

@@ -57,7 +57,7 @@ CONFIG_CP15_BARRIER_EMULATION=y
 CONFIG_SETEND_EMULATION=y
 CONFIG_RANDOMIZE_BASE=y
 # CONFIG_RANDOMIZE_MODULE_REGION_FULL is not set
-CONFIG_CMDLINE="stack_depot_disable=on"
+CONFIG_CMDLINE="stack_depot_disable=on kasan.stacktrace=off"
 CONFIG_CMDLINE_EXTEND=y
 # CONFIG_DMI is not set
 CONFIG_PM_WAKELOCKS=y
@@ -602,6 +602,8 @@ CONFIG_MAGIC_SYSRQ=y
 CONFIG_PAGE_OWNER=y
 CONFIG_DEBUG_STACK_USAGE=y
 CONFIG_DEBUG_MEMORY_INIT=y
+CONFIG_KASAN=y
+CONFIG_KASAN_HW_TAGS=y
 CONFIG_PANIC_ON_OOPS=y
 CONFIG_PANIC_TIMEOUT=-1
 CONFIG_SOFTLOCKUP_DETECTOR=y