kasan: docs: update SW_TAGS implementation details section

Update the "Implementation details" section for SW_TAGS KASAN:

 - Clarify the introduction sentence.

 - Punctuation, readability, and other minor clean-ups.

Link: https://lkml.kernel.org/r/69b9b2e49d8cf789358fa24558be3fc0ce4ee32c.1615559068.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/dev-tools/kasan.rst

@@ -244,38 +244,37 @@ quarantine (see mm/kasan/quarantine.c for implementation).
 Software tag-based KASAN
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-Software tag-based KASAN requires software memory tagging support in the form
-of HWASan-like compiler instrumentation (see HWASan documentation for details).
-
-Software tag-based KASAN is currently only implemented for arm64 architecture.
+Software tag-based KASAN uses a software memory tagging approach to checking
+access validity. It is currently only implemented for the arm64 architecture.
 
 Software tag-based KASAN uses the Top Byte Ignore (TBI) feature of arm64 CPUs
-to store a pointer tag in the top byte of kernel pointers. Like generic KASAN
-it uses shadow memory to store memory tags associated with each 16-byte memory
-cell (therefore it dedicates 1/16th of the kernel memory for shadow memory).
+to store a pointer tag in the top byte of kernel pointers. It uses shadow memory
+to store memory tags associated with each 16-byte memory cell (therefore, it
+dedicates 1/16th of the kernel memory for shadow memory).
 
-On each memory allocation software tag-based KASAN generates a random tag, tags
-the allocated memory with this tag, and embeds this tag into the returned
+On each memory allocation, software tag-based KASAN generates a random tag, tags
+the allocated memory with this tag, and embeds the same tag into the returned
 pointer.
 
 Software tag-based KASAN uses compile-time instrumentation to insert checks
-before each memory access. These checks make sure that tag of the memory that
-is being accessed is equal to tag of the pointer that is used to access this
-memory. In case of a tag mismatch software tag-based KASAN prints a bug report.
+before each memory access. These checks make sure that the tag of the memory
+that is being accessed is equal to the tag of the pointer that is used to access
+this memory. In case of a tag mismatch, software tag-based KASAN prints a bug
+report.
 
-Software tag-based KASAN also has two instrumentation modes (outline, that
-emits callbacks to check memory accesses; and inline, that performs the shadow
+Software tag-based KASAN also has two instrumentation modes (outline, which
+emits callbacks to check memory accesses; and inline, which performs the shadow
 memory checks inline). With outline instrumentation mode, a bug report is
-simply printed from the function that performs the access check. With inline
-instrumentation a brk instruction is emitted by the compiler, and a dedicated
-brk handler is used to print bug reports.
+printed from the function that performs the access check. With inline
+instrumentation, a ``brk`` instruction is emitted by the compiler, and a
+dedicated ``brk`` handler is used to print bug reports.
 
 Software tag-based KASAN uses 0xFF as a match-all pointer tag (accesses through
-pointers with 0xFF pointer tag aren't checked). The value 0xFE is currently
+pointers with the 0xFF pointer tag are not checked). The value 0xFE is currently
 reserved to tag freed memory regions.
 
-Software tag-based KASAN currently only supports tagging of
-kmem_cache_alloc/kmalloc and page_alloc memory.
+Software tag-based KASAN currently only supports tagging of slab and page_alloc
+memory.
 
 Hardware tag-based KASAN
 ~~~~~~~~~~~~~~~~~~~~~~~~