[PATCH v3 mm 13/13] kasan: clarify that only first bug is reported in HW_TAGS

Andrey Konovalov
2021-02-05T17:45:42Z

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@google.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