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

From: Marco Elver
Date: Mon Jul 12 2021 - 12:44:16 EST


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@xxxxxxxxxx>
> ---
> 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