linux-kernel - [PATCH 10/11] kasan: docs: update ignoring accesses section

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Date:   Thu, 11 Mar 2021 22:37:22 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH 10/11] kasan: docs: update ignoring accesses section

Update the "Ignoring accesses" section in KASAN documentation:

- Mention kasan_disable/enable_current().
- Mention kasan_reset_tag()/page_kasan_tag_reset().
- A punctuation clean-up.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 Documentation/dev-tools/kasan.rst | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 2b61d90e136f..6628b133c9ad 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -368,7 +368,7 @@ Ignoring accesses
 ~~~~~~~~~~~~~~~~~
 
 Software KASAN modes use compiler instrumentation to insert validity checks.
-Such instrumentation might be incompatible with some part of the kernel, and
+Such instrumentation might be incompatible with some parts 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
 Makefile:
@@ -381,6 +381,19 @@ Makefile:
 
     KASAN_SANITIZE := n
 
+Other parts of the kernel might access metadata for allocated objects. Normally,
+KASAN detects and reports such accesses, but in certain cases (e.g., in memory
+allocators) these accesses are valid. Disabling instrumentation for memory
+allocators files helps with accesses that happen directly in that code for
+software KASAN modes. But it does not help when the accesses happen indirectly
+(through generic function calls) or with the hardware tag-based mode that does
+not use compiler instrumentation.
+
+To disable KASAN reports in a certain part of the kernel code:
+
+- For software modes, add a
+  ``kasan_disable_current()``/``kasan_enable_current()`` critical section.
+- For tag-based modes, use ``kasan_reset_tag()`` or ``page_kasan_tag_reset()``.
 
 Tests
 ~~~~~
-- 
2.31.0.rc2.261.g7f71774620-goog