* + kasan-docs-update-ignoring-accesses-section.patch added to -mm tree
@ 2021-03-12 18:36 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2021-03-12 18:36 UTC (permalink / raw)
To: andreyknvl, aryabinin, dvyukov, elver, glider, mm-commits
The patch titled
Subject: kasan: docs: update ignoring accesses section
has been added to the -mm tree. Its filename is
kasan-docs-update-ignoring-accesses-section.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kasan-docs-update-ignoring-accesses-section.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kasan-docs-update-ignoring-accesses-section.patch
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------------------------------------------------------
From: Andrey Konovalov <andreyknvl@google.com>
Subject: kasan: docs: update ignoring accesses section
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>
---
Documentation/dev-tools/kasan.rst | 34 ++++++++++++++++++++++++----
1 file changed, 30 insertions(+), 4 deletions(-)
--- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-ignoring-accesses-section
+++ a/Documentation/dev-tools/kasan.rst
@@ -368,12 +368,18 @@ 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
@@ -381,6 +387,26 @@ 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
~~~~~
_
Patches currently in -mm which might be from andreyknvl@google.com are
kasan-mm-fix-crash-with-hw_tags-and-debug_pagealloc.patch
kasan-fix-kasan_stack-dependency-for-hw_tags.patch
kasan-fix-per-page-tags-for-non-page_alloc-pages.patch
kasan-initialize-shadow-to-tag_invalid-for-sw_tags.patch
mm-kasan-dont-poison-boot-memory-with-tag-based-modes.patch
arm64-kasan-allow-to-init-memory-when-setting-tags.patch
kasan-init-memory-in-kasan_unpoison-for-hw_tags.patch
kasan-mm-integrate-page_alloc-init-with-hw_tags.patch
kasan-mm-integrate-slab-init_on_alloc-with-hw_tags.patch
kasan-mm-integrate-slab-init_on_free-with-hw_tags.patch
kasan-docs-clean-up-sections.patch
kasan-docs-update-overview-section.patch
kasan-docs-update-usage-section.patch
kasan-docs-update-error-reports-section.patch
kasan-docs-update-boot-parameters-section.patch
kasan-docs-update-generic-implementation-details-section.patch
kasan-docs-update-sw_tags-implementation-details-section.patch
kasan-docs-update-hw_tags-implementation-details-section.patch
kasan-docs-update-shadow-memory-section.patch
kasan-docs-update-ignoring-accesses-section.patch
kasan-docs-update-tests-section.patch
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