Lines Matching +full:in +full:- +full:memory
5 --------
7 KernelAddressSANitizer (KASAN) is a dynamic memory error detector designed to
8 find out-of-bound and use-after-free bugs. KASAN has two modes: generic KASAN
9 (similar to userspace ASan) and software tag-based KASAN (similar to userspace
12 KASAN uses compile-time instrumentation to insert validity checks before every
13 memory access, and therefore requires a compiler version that supports that.
15 Generic KASAN is supported in both GCC and Clang. With GCC it requires version
17 out-of-bounds accesses for global variables is only supported since Clang 11.
19 Tag-based KASAN is only supported in Clang.
22 and riscv architectures, and tag-based KASAN is supported only for arm64.
25 -----
32 CONFIG_KASAN_SW_TAGS (to enable software tag-based KASAN).
36 smaller binary while the latter is 1.1 - 2 times faster.
38 Both KASAN modes work with both SLUB and SLAB memory allocators.
47 - For a single file (e.g. main.o)::
51 - For all files in one directory::
58 A typical out-of-bounds access generic KASAN report looks like this::
61 BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
64 CPU: 1 PID: 2760 Comm: insmod Not tainted 4.19.0-rc3+ #698
65 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
112 which belongs to the cache kmalloc-128 of size 128
114 128-byte region [ffff8801f44ec300, ffff8801f44ec380)
122 Memory state around the buggy address:
133 access, a stack trace of where the accessed memory was allocated (in case bad
135 freed (in case of a use-after-free bug report). Next comes a description of
136 the accessed slab object and information about the accessed memory page.
138 In the last section the report shows memory state around the accessed address.
141 The state of each 8 aligned bytes of memory is encoded in one shadow byte.
144 of the corresponding memory region are accessible; number N (1 <= N <= 7) means
145 that the first N bytes are accessible, and other (8 - N) bytes are not;
146 any negative value indicates that the entire 8-byte word is inaccessible.
148 inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
150 In the report above the arrows point to the shadow byte 03, which means that
153 For tag-based KASAN this last report section shows the memory tags around the
158 ----------------------
163 From a high level, our approach to memory error detection is similar to that
164 of kmemcheck: use shadow memory to record whether each byte of memory is safe
165 to access, and use compile-time instrumentation to insert checks of shadow
166 memory on each memory access.
168 Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
170 translate a memory address to its corresponding shadow address.
183 Compile-time instrumentation is used to insert memory access checks. Compiler
185 memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
186 access is valid or not by checking corresponding shadow memory.
189 function calls GCC directly inserts the code to check the shadow memory.
190 This option significantly enlarges kernel but it gives x1.1-x2 performance
193 Generic KASAN prints up to 2 call_rcu() call stacks in reports, the last one
196 Software tag-based KASAN
199 Tag-based KASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to
200 store a pointer tag in the top byte of kernel pointers. Like generic KASAN it
201 uses shadow memory to store memory tags associated with each 16-byte memory
202 cell (therefore it dedicates 1/16th of the kernel memory for shadow memory).
204 On each memory allocation tag-based KASAN generates a random tag, tags the
205 allocated memory with this tag, and embeds this tag into the returned pointer.
206 Software tag-based KASAN uses compile-time instrumentation to insert checks
207 before each memory access. These checks make sure that tag of the memory that
209 memory. In case of a tag mismatch tag-based KASAN prints a bug report.
211 Software tag-based KASAN also has two instrumentation modes (outline, that
212 emits callbacks to check memory accesses; and inline, that performs the shadow
213 memory checks inline). With outline instrumentation mode, a bug report is
218 A potential expansion of this mode is a hardware tag-based mode, which would
219 use hardware memory tagging support instead of compiler instrumentation and
220 manual shadow memory manipulation.
222 What memory accesses are sanitised by KASAN?
223 --------------------------------------------
225 The kernel maps memory in a number of different parts of the address
231 real memory to support a real shadow region for every address that
237 By default, architectures only map real memory over the shadow region
239 other areas - such as vmalloc and vmemmap space - a single read-only
240 page is mapped over the shadow area. This read-only shadow page
241 declares all memory accesses as permitted.
243 This presents a problem for modules: they do not live in the linear
244 mapping, but in a dedicated module space. By hooking in to the module
245 allocator, KASAN can temporarily map real shadow memory to cover
250 lives in vmalloc space, it will be shadowed by the read-only page, and
258 cost of greater memory usage. Currently this is only supported on x86.
261 allocating real shadow memory to back the mappings.
263 Most mappings in vmalloc space are small, requiring less than a full
270 a backing page when a mapping in vmalloc space uses a particular page
274 We hook in to the vmap infrastructure to lazily clean up unused shadow
275 memory.
280 unmapped. This will require changes in arch-specific code.
286 --------------------------------------------------
297 ok 28 - kmalloc_double_kzfree
303 not ok 4 - kmalloc_large_oob_right
308 Expected kasan_data->report_expected == kasan_data->report_found, but
309 kasan_data->report_expected == 1
310 kasan_data->report_found == 0
311 not ok 28 - kmalloc_double_kzfree
316 ok 1 - kasan
320 not ok 1 - kasan
329 (2) Built-In
332 With ``CONFIG_KUNIT`` built-in, ``CONFIG_KASAN_KUNIT_TEST`` can be built-in
334 tests enabled will run and print the results at boot as a late-init
340 With ``CONFIG_KUNIT`` and ``CONFIG_KASAN_KUNIT_TEST`` built-in, we can also
342 tests in a more readable way. This will not print the KASAN reports
343 …cumentation <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ for more up-to-d…
346 .. _KUnit: https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html
351 ``CONFIG_KASAN`` built-in. The type of error expected and the