docs: sphinxify kasan.txt and move to dev-tools

No textual changes beyond formatting.

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 171 deletions

diff --git a/Documentation/kasan.txt b/Documentation/kasan.txt
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-KernelAddressSanitizer (KASAN)
-==============================
-
-0. Overview
-===========
-
-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 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.
-
-1. Usage
-========
-
-To enable KASAN configure kernel with:
-
-	  CONFIG_KASAN = y
-
-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.
-
-KASAN works with both SLUB and SLAB memory allocators.
-For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
-
-To disable instrumentation for specific files or directories, add a line
-similar to the following to the respective kernel Makefile:
-
-        For a single file (e.g. main.o):
-                KASAN_SANITIZE_main.o := n
-
-        For all files in one directory:
-                KASAN_SANITIZE := n
-
-1.1 Error reports
-=================
-
-A typical out of bounds access report looks like this:
-
-==================================================================
-BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
-Write of size 1 by task modprobe/1689
-=============================================================================
-BUG kmalloc-128 (Not tainted): kasan error
------------------------------------------------------------------------------
-
-Disabling lock debugging due to kernel taint
-INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
- __slab_alloc+0x4b4/0x4f0
- kmem_cache_alloc_trace+0x10b/0x190
- kmalloc_oob_right+0x3d/0x75 [test_kasan]
- init_module+0x9/0x47 [test_kasan]
- do_one_initcall+0x99/0x200
- load_module+0x2cb3/0x3b20
- SyS_finit_module+0x76/0x80
- system_call_fastpath+0x12/0x17
-INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
-INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
-
-Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
-Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.
-Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc                          ........
-Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
-CPU: 0 PID: 1689 Comm: modprobe Tainted: G    B          3.18.0-rc1-mm1+ #98
-Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
- ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
- ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
- ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
-Call Trace:
- [<ffffffff81cc68ae>] dump_stack+0x46/0x58
- [<ffffffff811fd848>] print_trailer+0xf8/0x160
- [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
- [<ffffffff811ff0f5>] object_err+0x35/0x40
- [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
- [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
- [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
- [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
- [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
- [<ffffffff8120a995>] __asan_store1+0x75/0xb0
- [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
- [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
- [<ffffffff810002d9>] do_one_initcall+0x99/0x200
- [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
- [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
- [<ffffffff8110fd70>] ? m_show+0x240/0x240
- [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
- [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
-Memory state around the buggy address:
- ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
- ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
->ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
-                                                 ^
- ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
- ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
- ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
-==================================================================
-
-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 understanding of how KASAN works.
-
-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;
-any negative value indicates that the entire 8-byte word is inaccessible.
-We use different negative values to distinguish between different kinds of
-inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
-
-In the report above the arrows point to the shadow byte 03, which means that
-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
-to access, and use compile-time instrumentation to check shadow memory on each
-memory access.
-
-AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
-(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
-offset to translate a memory address to its corresponding shadow address.
-
-Here is the function which translates an address to its corresponding shadow
-address:
-
-static inline void *kasan_mem_to_shadow(const void *addr)
-{
-	return ((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
-		+ KASAN_SHADOW_OFFSET;
-}
-
-where KASAN_SHADOW_SCALE_SHIFT = 3.
-
-Compile-time instrumentation used for checking memory accesses. Compiler inserts
-function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
-access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
-valid or not by checking corresponding shadow memory.
-
-GCC 5.0 has possibility to perform inline instrumentation. Instead of making
-function calls GCC directly inserts the code to check the shadow memory.
-This option significantly enlarges kernel but it gives x1.1-x2 performance
-boost over outline instrumented kernel.