aboutsummaryrefslogtreecommitdiff
path: root/Documentation
diff options
context:
space:
mode:
authorAndrey Konovalov <andreyknvl@google.com>2015-11-05 18:51:06 -0800
committerAlex Shi <alex.shi@linaro.org>2016-04-11 22:59:21 +0800
commitfd2385c42871840041a1d7b7b69c853311283a3b (patch)
tree007c75ba1251655dcc8abf8061a036c7c40949ec /Documentation
parentb05ec6e4ceda525c973a2fb383efad932f598502 (diff)
downloadlinux-linaro-stable-fd2385c42871840041a1d7b7b69c853311283a3b.tar.gz
kasan: various fixes in documentation
[akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Konstantin Serebryany <kcc@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> (cherry picked from commit 0295fd5d570626817d10deadf5a2ad5e49c36a1d) Signed-off-by: Alex Shi <alex.shi@linaro.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/kasan.txt43
1 files changed, 22 insertions, 21 deletions
diff --git a/Documentation/kasan.txt b/Documentation/kasan.txt
index 4692241789b1..4e906a091c60 100644
--- a/Documentation/kasan.txt
+++ b/Documentation/kasan.txt
@@ -1,32 +1,31 @@
-Kernel address sanitizer
-================
+KernelAddressSanitizer (KASAN)
+==============================
0. Overview
===========
-Kernel Address sanitizer (KASan) is a dynamic memory error detector. It provides
+KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
a fast and comprehensive solution for finding use-after-free and out-of-bounds
bugs.
-KASan uses compile-time instrumentation for checking every memory access,
-therefore you will need a gcc version of 4.9.2 or later. KASan could detect out
-of bounds accesses to stack or global variables, but only if gcc 5.0 or later was
-used to built the kernel.
+KASAN uses compile-time instrumentation for checking every memory access,
+therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
+required for detection of out-of-bounds accesses to stack or global variables.
-Currently KASan is supported only for x86_64 architecture and requires that the
-kernel be built with the SLUB allocator.
+Currently KASAN is supported only for x86_64 architecture and requires the
+kernel to be built with the SLUB allocator.
1. Usage
-=========
+========
To enable KASAN configure kernel with:
CONFIG_KASAN = y
-and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline/inline
-is compiler instrumentation types. The former produces smaller binary the
-latter is 1.1 - 2 times faster. Inline instrumentation requires a gcc version
-of 5.0 or later.
+and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
+inline are compiler instrumentation types. The former produces smaller binary
+the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
+version 5.0 or later.
Currently KASAN works only with the SLUB memory allocator.
For better bug detection and nicer report, enable CONFIG_STACKTRACE and put
@@ -42,7 +41,7 @@ similar to the following to the respective kernel Makefile:
KASAN_SANITIZE := n
1.1 Error reports
-==========
+=================
A typical out of bounds access report looks like this:
@@ -119,14 +118,16 @@ Memory state around the buggy address:
ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
-First sections describe slub object where bad access happened.
-See 'SLUB Debug output' section in Documentation/vm/slub.txt for details.
+The header of the report discribe what kind of bug happened and what kind of
+access caused it. It's followed by the description of the accessed slub object
+(see 'SLUB Debug output' section in Documentation/vm/slub.txt for details) and
+the description of the accessed memory page.
In the last section the report shows memory state around the accessed address.
-Reading this part requires some more understanding of how KASAN works.
+Reading this part requires some understanding of how KASAN works.
-Each 8 bytes of memory are encoded in one shadow byte as accessible,
-partially accessible, freed or they can be part of a redzone.
+The state of each 8 aligned bytes of memory is encoded in one shadow byte.
+Those 8 bytes can be accessible, partially accessible, freed or be a redzone.
We use the following encoding for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are accessible; number N (1 <= N <= 7) means
that the first N bytes are accessible, and other (8 - N) bytes are not;
@@ -139,7 +140,7 @@ the accessed address is partially accessible.
2. Implementation details
-========================
+=========================
From a high level, our approach to memory error detection is similar to that
of kmemcheck: use shadow memory to record whether each byte of memory is safe