path: root/Documentation
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authorAlex Shi <alex.shi@linaro.org>2016-04-27 09:52:15 +0800
committerAlex Shi <alex.shi@linaro.org>2016-04-27 09:52:15 +0800
commite0ac66e00b01f6ff4e8274a4b5c008a26583c1b9 (patch)
treec845d5e80991f0eef3a38381036c8261baffb08a /Documentation
parente9cd0f1ce300f433a478bd1973dea112b5fbb800 (diff)
parent7b44c3df0b89d05c80e15eb0522a21d033d1314f (diff)
Merge branch 'v3.18/topic/KASAN' into linux-linaro-lsk-v3.18lsk-v3.18-16.04
Diffstat (limited to 'Documentation')
3 files changed, 175 insertions, 1 deletions
diff --git a/Documentation/kasan.txt b/Documentation/kasan.txt
new file mode 100644
index 000000000000..58b72fbf450d
--- /dev/null
+++ b/Documentation/kasan.txt
@@ -0,0 +1,172 @@
+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
+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 the
+kernel to be built with the SLUB allocator.
+1. Usage
+To enable KASAN configure kernel with:
+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 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:
+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 witch translate an address to its corresponding shadow
+static inline void *kasan_mem_to_shadow(const void *addr)
+ return ((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
+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.
diff --git a/Documentation/video4linux/v4l2-pci-skeleton.c b/Documentation/video4linux/v4l2-pci-skeleton.c
index 006721e43b2a..7bd1b975bfd2 100644
--- a/Documentation/video4linux/v4l2-pci-skeleton.c
+++ b/Documentation/video4linux/v4l2-pci-skeleton.c
@@ -42,7 +42,6 @@
MODULE_AUTHOR("Hans Verkuil");
-MODULE_DEVICE_TABLE(pci, skeleton_pci_tbl);
* struct skeleton - All internal data for one instance of device
@@ -95,6 +94,7 @@ static const struct pci_device_id skeleton_pci_tbl[] = {
{ 0, }
+MODULE_DEVICE_TABLE(pci, skeleton_pci_tbl);
* HDTV: this structure has the capabilities of the HDTV receiver.
diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index 052ee643a32e..05712ac83e38 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -12,6 +12,8 @@ ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
... unused hole ...
+ffffec0000000000 - fffffc0000000000 (=44 bits) kasan shadow memory (16TB)
+... unused hole ...
ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
... unused hole ...
ffffffff80000000 - ffffffffa0000000 (=512 MB) kernel text mapping, from phys 0