The patch titled
Subject: kasan: docs: update SW_TAGS implementation details section
has been added to the -mm tree. Its filename is
kasan-docs-update-sw_tags-implementation-details-section.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kasan-docs-update-sw_tags-implementation-details-section.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kasan-docs-update-sw_tags-implementation-details-section.patch
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------------------------------------------------------
From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/dev-tools/kasan.rst | 39 +++++++++++++---------------
1 file changed, 19 insertions(+), 20 deletions(-)
--- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-sw_tags-implementation-details-section
+++ a/Documentation/dev-tools/kasan.rst
@@ -235,38 +235,37 @@ quarantine (see mm/kasan/quarantine.c fo
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
~~~~~~~~~~~~~~~~~~~~~~~~
_
Patches currently in -mm which might be from andreyknvl@xxxxxxxxxx are
kasan-mm-fix-crash-with-hw_tags-and-debug_pagealloc.patch
kasan-fix-kasan_stack-dependency-for-hw_tags.patch
kasan-fix-per-page-tags-for-non-page_alloc-pages.patch
kasan-initialize-shadow-to-tag_invalid-for-sw_tags.patch
mm-kasan-dont-poison-boot-memory-with-tag-based-modes.patch
arm64-kasan-allow-to-init-memory-when-setting-tags.patch
kasan-init-memory-in-kasan_unpoison-for-hw_tags.patch
kasan-mm-integrate-page_alloc-init-with-hw_tags.patch
kasan-mm-integrate-slab-init_on_alloc-with-hw_tags.patch
kasan-mm-integrate-slab-init_on_free-with-hw_tags.patch
kasan-docs-clean-up-sections.patch
kasan-docs-update-overview-section.patch
kasan-docs-update-usage-section.patch
kasan-docs-update-error-reports-section.patch
kasan-docs-update-boot-parameters-section.patch
kasan-docs-update-generic-implementation-details-section.patch
kasan-docs-update-sw_tags-implementation-details-section.patch
kasan-docs-update-hw_tags-implementation-details-section.patch
kasan-docs-update-shadow-memory-section.patch
kasan-docs-update-ignoring-accesses-section.patch
kasan-docs-update-tests-section.patch
