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

Marco Elver
2021-02-08T11:24:23Z

On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote:
> 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>

Reviewed-by: Marco Elver <elver@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
>