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Subject[PATCH] kasan: fix HW_TAGS boot parameters
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The initially proposed KASAN command line parameters are redundant.

This change drops the complex "kasan.mode=off/prod/full" parameter
and adds a simpler kill switch "kasan=off/on" instead. The new parameter
together with the already existing ones provides a cleaner way to
express the same set of features.

The full set of parameters with this change:

kasan=off/on - whether KASAN is enabled
kasan.fault=report/panic - whether to only print a report or also panic
kasan.stacktrace=off/on - whether to collect alloc/free stack traces

Default values:

kasan=on
kasan.fault=report
kasan.stacktrace=on (if CONFIG_DEBUG_KERNEL=y)
kasan.stacktrace=off (otherwise)

Link: https://linux-review.googlesource.com/id/Ib3694ed90b1e8ccac6cf77dfd301847af4aba7b8
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
Documentation/dev-tools/kasan.rst | 27 +++--------
mm/kasan/hw_tags.c | 77 +++++++++++++------------------
2 files changed, 38 insertions(+), 66 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 0fc3fb1860c4..1651d961f06a 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -160,29 +160,14 @@ 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.

-The things that can be controlled are:
+- ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).

-1. Whether KASAN is enabled at all.
-2. Whether KASAN collects and saves alloc/free stacks.
-3. Whether KASAN panics on a detected bug or not.
+- ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
+ traces collection (default: ``on`` for ``CONFIG_DEBUG_KERNEL=y``, otherwise
+ ``off``).

-The ``kasan.mode`` boot parameter allows to choose one of three main modes:
-
-- ``kasan.mode=off`` - KASAN is disabled, no tag checks are performed
-- ``kasan.mode=prod`` - only essential production features are enabled
-- ``kasan.mode=full`` - all KASAN features are enabled
-
-The chosen mode provides default control values for the features mentioned
-above. However it's also possible to override the default values by providing:
-
-- ``kasan.stacktrace=off`` or ``=on`` - enable alloc/free stack collection
- (default: ``on`` for ``mode=full``,
- otherwise ``off``)
-- ``kasan.fault=report`` or ``=panic`` - only print KASAN report or also panic
- (default: ``report``)
-
-If ``kasan.mode`` parameter is not provided, it defaults to ``full`` when
-``CONFIG_DEBUG_KERNEL`` is enabled, and to ``prod`` otherwise.
+- ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
+ report or also panic the kernel (default: ``report``).

For developers
~~~~~~~~~~~~~~
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 55bd6f09c70f..e529428e7a11 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -19,11 +19,10 @@

#include "kasan.h"

-enum kasan_arg_mode {
- KASAN_ARG_MODE_DEFAULT,
- KASAN_ARG_MODE_OFF,
- KASAN_ARG_MODE_PROD,
- KASAN_ARG_MODE_FULL,
+enum kasan_arg {
+ KASAN_ARG_DEFAULT,
+ KASAN_ARG_OFF,
+ KASAN_ARG_ON,
};

enum kasan_arg_stacktrace {
@@ -38,7 +37,7 @@ enum kasan_arg_fault {
KASAN_ARG_FAULT_PANIC,
};

-static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
+static enum kasan_arg kasan_arg __ro_after_init;
static enum kasan_arg_stacktrace kasan_arg_stacktrace __ro_after_init;
static enum kasan_arg_fault kasan_arg_fault __ro_after_init;

@@ -52,26 +51,24 @@ DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
/* Whether panic or disable tag checking on fault. */
bool kasan_flag_panic __ro_after_init;

-/* kasan.mode=off/prod/full */
-static int __init early_kasan_mode(char *arg)
+/* kasan=off/on */
+static int __init early_kasan_flag(char *arg)
{
if (!arg)
return -EINVAL;

if (!strcmp(arg, "off"))
- kasan_arg_mode = KASAN_ARG_MODE_OFF;
- else if (!strcmp(arg, "prod"))
- kasan_arg_mode = KASAN_ARG_MODE_PROD;
- else if (!strcmp(arg, "full"))
- kasan_arg_mode = KASAN_ARG_MODE_FULL;
+ kasan_arg = KASAN_ARG_OFF;
+ else if (!strcmp(arg, "on"))
+ kasan_arg = KASAN_ARG_ON;
else
return -EINVAL;

return 0;
}
-early_param("kasan.mode", early_kasan_mode);
+early_param("kasan", early_kasan_flag);

-/* kasan.stack=off/on */
+/* kasan.stacktrace=off/on */
static int __init early_kasan_flag_stacktrace(char *arg)
{
if (!arg)
@@ -113,8 +110,8 @@ void kasan_init_hw_tags_cpu(void)
* as this function is only called for MTE-capable hardware.
*/

- /* If KASAN is disabled, do nothing. */
- if (kasan_arg_mode == KASAN_ARG_MODE_OFF)
+ /* If KASAN is disabled via command line, don't initialize it. */
+ if (kasan_arg == KASAN_ARG_OFF)
return;

hw_init_tags(KASAN_TAG_MAX);
@@ -124,43 +121,28 @@ void kasan_init_hw_tags_cpu(void)
/* kasan_init_hw_tags() is called once on boot CPU. */
void __init kasan_init_hw_tags(void)
{
- /* If hardware doesn't support MTE, do nothing. */
+ /* If hardware doesn't support MTE, don't initialize KASAN. */
if (!system_supports_mte())
return;

- /* Choose KASAN mode if kasan boot parameter is not provided. */
- if (kasan_arg_mode == KASAN_ARG_MODE_DEFAULT) {
- if (IS_ENABLED(CONFIG_DEBUG_KERNEL))
- kasan_arg_mode = KASAN_ARG_MODE_FULL;
- else
- kasan_arg_mode = KASAN_ARG_MODE_PROD;
- }
-
- /* Preset parameter values based on the mode. */
- switch (kasan_arg_mode) {
- case KASAN_ARG_MODE_DEFAULT:
- /* Shouldn't happen as per the check above. */
- WARN_ON(1);
- return;
- case KASAN_ARG_MODE_OFF:
- /* If KASAN is disabled, do nothing. */
+ /* If KASAN is disabled via command line, don't initialize it. */
+ if (kasan_arg == KASAN_ARG_OFF)
return;
- case KASAN_ARG_MODE_PROD:
- static_branch_enable(&kasan_flag_enabled);
- break;
- case KASAN_ARG_MODE_FULL:
- static_branch_enable(&kasan_flag_enabled);
- static_branch_enable(&kasan_flag_stacktrace);
- break;
- }

- /* Now, optionally override the presets. */
+ /* Enable KASAN. */
+ static_branch_enable(&kasan_flag_enabled);

switch (kasan_arg_stacktrace) {
case KASAN_ARG_STACKTRACE_DEFAULT:
+ /*
+ * Default to enabling stack trace collection for
+ * debug kernels.
+ */
+ if (IS_ENABLED(CONFIG_DEBUG_KERNEL))
+ static_branch_enable(&kasan_flag_stacktrace);
break;
case KASAN_ARG_STACKTRACE_OFF:
- static_branch_disable(&kasan_flag_stacktrace);
+ /* Do nothing, kasan_flag_stacktrace keeps its default value. */
break;
case KASAN_ARG_STACKTRACE_ON:
static_branch_enable(&kasan_flag_stacktrace);
@@ -169,11 +151,16 @@ void __init kasan_init_hw_tags(void)

switch (kasan_arg_fault) {
case KASAN_ARG_FAULT_DEFAULT:
+ /*
+ * Default to no panic on report.
+ * Do nothing, kasan_flag_panic keeps its default value.
+ */
break;
case KASAN_ARG_FAULT_REPORT:
- kasan_flag_panic = false;
+ /* Do nothing, kasan_flag_panic keeps its default value. */
break;
case KASAN_ARG_FAULT_PANIC:
+ /* Enable panic on report. */
kasan_flag_panic = true;
break;
}
--
2.30.0.284.gd98b1dd5eaa7-goog
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