linux-kernel - [PATCH v3 mm 13/13] kasan: clarify that only first bug is reported in HW

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Message-Id: <00383ba88a47c3f8342d12263c24bdf95527b07d.1612546384.git.andreyknvl@google.com>
Date:   Fri,  5 Feb 2021 18:34:47 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Cc:     Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v3 mm 13/13] kasan: clarify that only first bug is reported in HW_TAGS

Hwardware tag-based KASAN only reports the first found bug. After that MTE
tag checking gets disabled. Clarify this in comments and documentation.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 Documentation/dev-tools/kasan.rst | 8 ++++++--
 mm/kasan/hw_tags.c                | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index e022b7506e37..1faabbe23e09 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -155,7 +155,7 @@ Boot parameters
 ~~~~~~~~~~~~~~~
 
 Hardware tag-based KASAN mode (see the section about various modes below) is
-intended for use in production as a security mitigation. Therefore it supports
+intended for use in production as a security mitigation. Therefore, it supports
 boot parameters that allow to disable KASAN competely or otherwise control
 particular KASAN features.
 
@@ -166,7 +166,8 @@ particular KASAN features.
   ``off``).
 
 - ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
-  report or also panic the kernel (default: ``report``).
+  report or also panic the kernel (default: ``report``). Note, that tag
+  checking gets disabled after the first reported bug.
 
 For developers
 ~~~~~~~~~~~~~~
@@ -296,6 +297,9 @@ Note, that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI being
 enabled. Even when kasan.mode=off is provided, or when the hardware doesn't
 support MTE (but supports TBI).
 
+Hardware tag-based KASAN only reports the first found bug. After that MTE tag
+checking gets disabled.
+
 What memory accesses are sanitised by KASAN?
 --------------------------------------------
 
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index e529428e7a11..6c9285c906b8 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -48,7 +48,7 @@ EXPORT_SYMBOL(kasan_flag_enabled);
 /* Whether to collect alloc/free stack traces. */
 DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
 
-/* Whether panic or disable tag checking on fault. */
+/* Whether to panic or print a report and disable tag checking on fault. */
 bool kasan_flag_panic __ro_after_init;
 
 /* kasan=off/on */
-- 
2.30.0.365.g02bc693789-goog