arm64: kasan: allow enabling in-kernel MTE

Hardware tag-based KASAN relies on Memory Tagging Extension (MTE) feature
and requires it to be enabled.  MTE supports

This patch adds a new mte_enable_kernel() helper, that enables MTE in
Synchronous mode in EL1 and is intended to be called from KASAN runtime
during initialization.

The Tag Checking operation causes a synchronous data abort as a
consequence of a tag check fault when MTE is configured in synchronous
mode.

As part of this change enable match-all tag for EL1 to allow the kernel to
access user pages without faulting.  This is required because the kernel
does not have knowledge of the tags set by the user in a page.

Note: For MTE, the TCF bit field in SCTLR_EL1 affects only EL1 in a
similar way as TCF0 affects EL0.

MTE that is built on top of the Top Byte Ignore (TBI) feature hence we
enable it as part of this patch as well.

Link: https://lkml.kernel.org/r/7352b0a0899af65c2785416c8ca6bf3845b66fa1.1606161801.git.andreyknvl@google.com


Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>