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UPSTREAM: kasan: docs: update ignoring accesses section

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Update the "Ignoring accesses" section in KASAN documentation:

 - Mention __no_sanitize_address/noinstr.

 - Mention kasan_disable/enable_current().

 - Mention kasan_reset_tag()/page_kasan_tag_reset().

 - Readability and punctuation clean-ups.

Link: https://lkml.kernel.org/r/4531ba5f3eca61f6aade863c136778cc8c807a64.1615559068.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit fe547fca0c)
Bug: 217222520
Change-Id: Id2e6e54d7c00f447b39c934cb7cae3f78afb8fde
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
This commit is contained in:
Andrey Konovalov
2021-04-29 23:00:39 -07:00
parent 558cf9358a
commit bd5b44a8ac
1 changed files with 30 additions and 4 deletions
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34
Documentation/dev-tools/kasan.rst
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@@ -377,12 +377,18 @@ Ignoring accesses
~~~~~~~~~~~~~~~~~
Software KASAN modes use compiler instrumentation to insert validity checks.
Such instrumentation might be incompatible with some part of the kernel, and
therefore needs to be disabled. To disable instrumentation for specific files
or directories, add a line similar to the following to the respective kernel
Such instrumentation might be incompatible with some parts of the kernel, and
therefore needs to be disabled.
Other parts of the kernel might access metadata for allocated objects.
Normally, KASAN detects and reports such accesses, but in some cases (e.g.,
in memory allocators), these accesses are valid.
For software KASAN modes, to disable instrumentation for a specific file or
directory, add a ``KASAN_SANITIZE`` annotation to the respective kernel
Makefile:
- For a single file (e.g. main.o)::
- For a single file (e.g., main.o)::
KASAN_SANITIZE_main.o := n
@@ -390,6 +396,26 @@ Makefile:
KASAN_SANITIZE := n
For software KASAN modes, to disable instrumentation on a per-function basis,
use the KASAN-specific ``__no_sanitize_address`` function attribute or the
generic ``noinstr`` one.
Note that disabling compiler instrumentation (either on a per-file or a
per-function basis) makes KASAN ignore the accesses that happen directly in
that code for software KASAN modes. It does not help when the accesses happen
indirectly (through calls to instrumented functions) or with the hardware
tag-based mode that does not use compiler instrumentation.
For software KASAN modes, to disable KASAN reports in a part of the kernel code
for the current task, annotate this part of the code with a
``kasan_disable_current()``/``kasan_enable_current()`` section. This also
disables the reports for indirect accesses that happen through function calls.
For tag-based KASAN modes (include the hardware one), to disable access
checking, use ``kasan_reset_tag()`` or ``page_kasan_tag_reset()``. Note that
temporarily disabling access checking via ``page_kasan_tag_reset()`` requires
saving and restoring the per-page KASAN tag via
``page_kasan_tag``/``page_kasan_tag_set``.
Tests
~~~~~