From: Andrey Konovalov <andreyknvl@google.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
Dmitry Vyukov <dvyukov@google.com>,
kasan-dev@googlegroups.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v2 07/11] kasan: docs: update SW_TAGS implementation details section
Date: Fri, 12 Mar 2021 15:24:30 +0100 [thread overview]
Message-ID: <69b9b2e49d8cf789358fa24558be3fc0ce4ee32c.1615559068.git.andreyknvl@google.com> (raw)
In-Reply-To: <c2bbb56eaea80ad484f0ee85bb71959a3a63f1d7.1615559068.git.andreyknvl@google.com>
Update the "Implementation details" section for SW_TAGS KASAN:
- Clarify the introduction sentence.
- Punctuation, readability, and other minor clean-ups.
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
Documentation/dev-tools/kasan.rst | 39 +++++++++++++++----------------
1 file changed, 19 insertions(+), 20 deletions(-)
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 986410bf269f..5873d80cc1fd 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -235,38 +235,37 @@ 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
~~~~~~~~~~~~~~~~~~~~~~~~
--
2.31.0.rc2.261.g7f71774620-goog
next prev parent reply other threads:[~2021-03-12 14:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 14:24 [PATCH v2 01/11] kasan: docs: clean up sections Andrey Konovalov
2021-03-12 14:24 ` [PATCH v2 02/11] kasan: docs: update overview section Andrey Konovalov
2021-03-12 15:07 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 03/11] kasan: docs: update usage section Andrey Konovalov
2021-03-12 15:07 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 04/11] kasan: docs: update error reports section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 05/11] kasan: docs: update boot parameters section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 06/11] kasan: docs: update GENERIC implementation details section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` Andrey Konovalov [this message]
2021-03-12 15:09 ` [PATCH v2 07/11] kasan: docs: update SW_TAGS " Marco Elver
2021-03-12 14:24 ` [PATCH v2 08/11] kasan: docs: update HW_TAGS " Andrey Konovalov
2021-03-12 15:09 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 09/11] kasan: docs: update shadow memory section Andrey Konovalov
2021-03-12 15:09 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 10/11] kasan: docs: update ignoring accesses section Andrey Konovalov
2021-03-12 15:10 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 11/11] kasan: docs: update tests section Andrey Konovalov
2021-03-12 15:11 ` Marco Elver
2021-03-12 15:06 ` [PATCH v2 01/11] kasan: docs: clean up sections Marco Elver
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