--- /dev/null
-Currently KASAN is supported only for x86_64 architecture.
+ The Kernel Address Sanitizer (KASAN)
+ ====================================
+
+ 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 the x86_64 and arm64 architectures.
+
+ 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
+
+ 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.
+
+
+ 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.
projects / GitHub / MotorolaMobilityLLC / kernel-slsi.git / commitdiff