linux-kernel - Re: [PATCH] mm/kasan: move kasan.fault to mm/kasan/report.c

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Date:   Mon, 12 Jul 2021 18:44:04 +0200
From:   Marco Elver <elver@...gle.com>
To:     Woody Lin <woodylin@...gle.com>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/kasan: move kasan.fault to mm/kasan/report.c

On Mon, Jul 12, 2021 at 11:16PM +0800, 'Woody Lin' via kasan-dev wrote:
> Move the boot parameter 'kasan.fault' from hw_tags.c to report.c, so it
> can support all KASAN modes - generic, and both tag-based.
> 
> Signed-off-by: Woody Lin <woodylin@...gle.com>
> ---
>  Documentation/dev-tools/kasan.rst |  2 ++
>  mm/kasan/hw_tags.c                | 43 -------------------------------
>  mm/kasan/report.c                 | 29 ++++++++++++++++++---
>  3 files changed, 28 insertions(+), 46 deletions(-)
> 
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index 83ec4a556c19..ab8e27d45632 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -203,6 +203,8 @@ boot parameters that allow disabling KASAN or controlling its features.
>    report or also panic the kernel (default: ``report``). The panic happens even
>    if ``kasan_multi_shot`` is enabled.
>  
> +  Note: The boot parameter 'kasan.fault' is supported by all KASAN modes.

This documentation change seems hacked on. Could we change it like this:

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 83ec4a556c19..21dc03bc10a4 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -181,9 +181,16 @@ By default, KASAN prints a bug report only for the first invalid memory access.
 With ``kasan_multi_shot``, KASAN prints a report on every invalid access. This
 effectively disables ``panic_on_warn`` for KASAN reports.
 
+Alternatively, independent of ``panic_on_warn`` the ``kasan.fault=`` boot
+parameter can be used to control panic and reporting behaviour:
+
+- ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
+  report or also panic the kernel (default: ``report``). The panic happens even
+  if ``kasan_multi_shot`` is enabled.
+
 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
-boot parameters that allow disabling KASAN or controlling its features.
+additional boot parameters that allow disabling KASAN or controlling features:
 
 - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
 
@@ -199,10 +206,6 @@ boot parameters that allow disabling KASAN or controlling its features.
 - ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
   traces collection (default: ``on``).
 
-- ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
-  report or also panic the kernel (default: ``report``). The panic happens even
-  if ``kasan_multi_shot`` is enabled.
-
 Implementation details
 ----------------------
 

[...]
> -/* Whether to panic or print a report and disable tag checking on fault. */
> -bool kasan_flag_panic __ro_after_init;

There's also an extern declaration in kasan.h, which should be removed.

Thanks,
-- Marco