Lines Matching +full:in +full:- +full:memory
5 --------
7 Kernel Address Sanitizer (KASAN) is a dynamic memory safety error detector
8 designed to find out-of-bounds and use-after-free bugs.
13 2. Software Tag-Based KASAN
14 3. Hardware Tag-Based KASAN
18 architectures, but it has significant performance and memory overheads.
20 Software Tag-Based KASAN or SW_TAGS KASAN, enabled with CONFIG_KASAN_SW_TAGS,
22 This mode is only supported for arm64, but its moderate memory overhead allows
23 using it for testing on memory-restricted devices with real workloads.
25 Hardware Tag-Based KASAN or HW_TAGS KASAN, enabled with CONFIG_KASAN_HW_TAGS,
26 is the mode intended to be used as an in-field memory bug detector or as a
28 (Memory Tagging Extension), but it has low memory and performance overheads and
29 thus can be used in production.
31 For details about the memory and performance impact of each KASAN mode, see the
34 The Generic and the Software Tag-Based modes are commonly referred to as the
35 software modes. The Software Tag-Based and the Hardware Tag-Based modes are
36 referred to as the tag-based modes.
39 -------
45 and loongarch, and the tag-based KASAN modes are supported only on arm64.
50 Software KASAN modes use compile-time instrumentation to insert validity checks
51 before every memory access and thus require a compiler version that provides
52 support for that. The Hardware Tag-Based mode relies on hardware to perform
53 these checks but still requires a compiler version that supports the memory
59 Software Tag-Based KASAN requires GCC 11+
62 Hardware Tag-Based KASAN requires GCC 10+ or Clang 12+.
64 Memory types
67 Generic KASAN supports finding bugs in all of slab, page_alloc, vmap, vmalloc,
68 stack, and global memory.
70 Software Tag-Based KASAN supports slab, page_alloc, vmalloc, and stack memory.
72 Hardware Tag-Based KASAN supports slab, page_alloc, and non-executable vmalloc
73 memory.
76 Hardware Tag-Based KASAN only supports SLUB.
79 -----
86 ``CONFIG_KASAN_SW_TAGS`` (to enable Software Tag-Based KASAN), and
87 ``CONFIG_KASAN_HW_TAGS`` (to enable Hardware Tag-Based KASAN).
103 By default, KASAN prints a bug report only for the first invalid memory access.
110 - ``kasan.fault=report``, ``=panic``, or ``=panic_on_write`` controls whether
114 Hardware Tag-Based KASAN, ``kasan.fault=panic_on_write`` always panics on
117 Software and Hardware Tag-Based KASAN modes (see the section about various
120 - ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
122 - ``kasan.stack_ring_size=<number of entries>`` specifies the number of entries
123 in the stack ring (default: ``32768``).
125 Hardware Tag-Based KASAN mode is intended for use in production as a security
129 - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
131 - ``kasan.mode=sync``, ``=async`` or ``=asymm`` controls whether KASAN
132 is configured in synchronous, asynchronous or asymmetric mode of
137 fault occurs, the information is stored in hardware (in the TFSR_EL1
143 - ``kasan.vmalloc=off`` or ``=on`` disables or enables tagging of vmalloc
146 - ``kasan.page_alloc.sample=<sampling interval>`` makes KASAN tag only every
152 Note that enabling this parameter makes Hardware Tag-Based KASAN skip checks
156 - ``kasan.page_alloc.sample.order=<minimum page order>`` specifies the minimum
169 BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
172 CPU: 1 PID: 2760 Comm: insmod Not tainted 4.19.0-rc3+ #698
173 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
220 which belongs to the cache kmalloc-128 of size 128
222 128-byte region [ffff8801f44ec300, ffff8801f44ec380)
230 Memory state around the buggy address:
241 where the accessed memory was allocated (in case a slab object was accessed),
242 and a stack trace of where the object was freed (in case of a use-after-free
244 information about the accessed memory page.
246 In the end, the report shows the memory state around the accessed address.
247 Internally, KASAN tracks memory state separately for each memory granule, which
248 is either 8 or 16 aligned bytes depending on KASAN mode. Each number in the
249 memory state section of the report shows the state of one of the memory
252 For Generic KASAN, the size of each memory granule is 8. The state of each
253 granule is encoded in one shadow byte. Those 8 bytes can be accessible,
256 memory region are accessible; number N (1 <= N <= 7) means that the first N
257 bytes are accessible, and other (8 - N) bytes are not; any negative value
258 indicates that the entire 8-byte word is inaccessible. KASAN uses different
259 negative values to distinguish between different kinds of inaccessible memory
260 like redzones or freed memory (see mm/kasan/kasan.h).
262 In the report above, the arrow points to the shadow byte ``03``, which means
265 For tag-based KASAN modes, this last report section shows the memory tags around
268 Note that KASAN bug titles (like ``slab-out-of-bounds`` or ``use-after-free``)
269 are best-effort: KASAN prints the most probable bug type based on the limited
273 traces point to places in code that interacted with the object but that are not
274 directly present in the bad access stack trace. Currently, this includes
278 ----------------------
283 Software KASAN modes use shadow memory to record whether each byte of memory is
284 safe to access and use compile-time instrumentation to insert shadow memory
285 checks before each memory access.
287 Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (16TB
289 translate a memory address to its corresponding shadow address.
302 Compile-time instrumentation is used to insert memory access checks. Compiler
304 each memory access of size 1, 2, 4, 8, or 16. These functions check whether
305 memory accesses are valid or not by checking corresponding shadow memory.
308 directly inserts the code to check shadow memory. This option significantly
309 enlarges the kernel, but it gives an x1.1-x2 performance boost over the
310 outline-instrumented kernel.
315 Software Tag-Based KASAN
318 Software Tag-Based KASAN uses a software memory tagging approach to checking
321 Software Tag-Based KASAN uses the Top Byte Ignore (TBI) feature of arm64 CPUs
322 to store a pointer tag in the top byte of kernel pointers. It uses shadow memory
323 to store memory tags associated with each 16-byte memory cell (therefore, it
324 dedicates 1/16th of the kernel memory for shadow memory).
326 On each memory allocation, Software Tag-Based KASAN generates a random tag, tags
327 the allocated memory with this tag, and embeds the same tag into the returned
330 Software Tag-Based KASAN uses compile-time instrumentation to insert checks
331 before each memory access. These checks make sure that the tag of the memory
333 this memory. In case of a tag mismatch, Software Tag-Based KASAN prints a bug
336 Software Tag-Based KASAN also has two instrumentation modes (outline, which
337 emits callbacks to check memory accesses; and inline, which performs the shadow
338 memory checks inline). With outline instrumentation mode, a bug report is
343 Software Tag-Based KASAN uses 0xFF as a match-all pointer tag (accesses through
345 reserved to tag freed memory regions.
347 Hardware Tag-Based KASAN
350 Hardware Tag-Based KASAN is similar to the software mode in concept but uses
351 hardware memory tagging support instead of compiler instrumentation and
352 shadow memory.
354 Hardware Tag-Based KASAN is currently only implemented for arm64 architecture
355 and based on both arm64 Memory Tagging Extension (MTE) introduced in ARMv8.5
358 Special arm64 instructions are used to assign memory tags for each allocation.
359 Same tags are assigned to pointers to those allocations. On every memory
360 access, hardware makes sure that the tag of the memory that is being accessed is
361 equal to the tag of the pointer that is used to access this memory. In case of a
364 Hardware Tag-Based KASAN uses 0xFF as a match-all pointer tag (accesses through
366 reserved to tag freed memory regions.
368 If the hardware does not support MTE (pre ARMv8.5), Hardware Tag-Based KASAN
369 will not be enabled. In this case, all KASAN boot parameters are ignored.
371 Note that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI being
375 Hardware Tag-Based KASAN only reports the first found bug. After that, MTE tag
378 Shadow memory
379 -------------
383 The kernel maps memory in several different parts of the address space.
385 memory to support a real shadow region for every address that could be
392 By default, architectures only map real memory over the shadow region
394 other areas - such as vmalloc and vmemmap space - a single read-only
395 page is mapped over the shadow area. This read-only shadow page
396 declares all memory accesses as permitted.
398 This presents a problem for modules: they do not live in the linear
399 mapping but in a dedicated module space. By hooking into the module
400 allocator, KASAN temporarily maps real shadow memory to cover them.
404 lives in vmalloc space, it will be shadowed by the read-only page, and
412 cost of greater memory usage. Currently, this is supported on x86,
416 allocating real shadow memory to back the mappings.
418 Most mappings in vmalloc space are small, requiring less than a full
425 a backing page when a mapping in vmalloc space uses a particular page
430 memory.
435 This will require changes in arch-specific code.
441 --------------
451 Normally, KASAN detects and reports such accesses, but in some cases (e.g.,
452 in memory allocators), these accesses are valid.
458 - For a single file (e.g., main.o)::
462 - For all files in one directory::
466 For software KASAN modes, to disable instrumentation on a per-function basis,
467 use the KASAN-specific ``__no_sanitize_address`` function attribute or the
470 Note that disabling compiler instrumentation (either on a per-file or a
471 per-function basis) makes KASAN ignore the accesses that happen directly in
474 Tag-Based KASAN, which does not use compiler instrumentation.
476 For software KASAN modes, to disable KASAN reports in a part of the kernel code
481 For tag-based KASAN modes, to disable access checking, use
484 restoring the per-page KASAN tag via ``page_kasan_tag``/``page_kasan_tag_set``.
490 certain types of memory corruptions. The tests consist of two parts:
494 automatically in a few different ways; see the instructions below.
501 Each KUnit-compatible KASAN test prints one of multiple KASAN reports if an
506 ok 28 - kmalloc_double_kzfree
512 not ok 4 - kmalloc_large_oob_right
517 KASAN failure expected in "kfree_sensitive(ptr)", but none occurred
518 not ok 44 - kmalloc_double_kzfree
523 ok 1 - kasan
527 not ok 1 - kasan
529 There are a few ways to run KUnit-compatible KASAN tests.
533 With ``CONFIG_KUNIT`` enabled, KASAN-KUnit tests can be built as a loadable
536 2. Built-In
538 With ``CONFIG_KUNIT`` built-in, KASAN-KUnit tests can be built-in as well.
539 In this case, the tests will run at boot as a late-init call.
543 With ``CONFIG_KUNIT`` and ``CONFIG_KASAN_KUNIT_TEST`` built-in, it is also
544 possible to use ``kunit_tool`` to see the results of KUnit tests in a more
546 See `KUnit documentation <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_
547 for more up-to-date information on ``kunit_tool``.
549 .. _KUnit: https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html