On Tue, Aug 9, 2016 at 1:34 AM, Jonathan Corbet <corbet@xxxxxxx> wrote:
> No textual changes beyond formatting.
>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Jonathan Corbet <corbet@xxxxxxx>
Acked-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> Documentation/dev-tools/kasan.rst | 173 ++++++++++++++++++++++++++++++++++++++
> Documentation/dev-tools/tools.rst | 1 +
> Documentation/kasan.txt | 171 -------------------------------------
> MAINTAINERS | 2 +-
> 4 files changed, 175 insertions(+), 172 deletions(-)
> create mode 100644 Documentation/dev-tools/kasan.rst
> delete mode 100644 Documentation/kasan.txt
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> new file mode 100644
> index 0000000..948d243
> --- /dev/null
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -0,0 +1,173 @@
> +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 x86_64 architecture.
> +
> +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.
> diff --git a/Documentation/dev-tools/tools.rst b/Documentation/dev-tools/tools.rst
> index 404d044..0500e65 100644
> --- a/Documentation/dev-tools/tools.rst
> +++ b/Documentation/dev-tools/tools.rst
> @@ -18,3 +18,4 @@ whole; patches welcome!
> sparse
> kcov
> gcov
> + kasan
> diff --git a/Documentation/kasan.txt b/Documentation/kasan.txt
> deleted file mode 100644
> index 7dd95b3..0000000
> --- a/Documentation/kasan.txt
> +++ /dev/null
> @@ -1,171 +0,0 @@
> -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.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index bb53779..2ffd7ed 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6587,7 +6587,7 @@ L: kasan-dev@xxxxxxxxxxxxxxxx
> S: Maintained
> F: arch/*/include/asm/kasan.h
> F: arch/*/mm/kasan_init*
> -F: Documentation/kasan.txt
> +F: Documentation/dev-tools/kasan.rst
> F: include/linux/kasan*.h
> F: lib/test_kasan.c
> F: mm/kasan/
> --
> 2.9.2
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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