Commit d85e6bac authored by Vincenzo Frascino's avatar Vincenzo Frascino
Browse files

kasan: Add KASAN mode kernel parameter



Architectures supported by KASAN_HW_TAGS can provide a sync or async mode
of execution. On an MTE enabled arm64 hw for example this can be identified
with the synchronous or asynchronous tagging mode of execution.
In synchronous mode, an exception is triggered if a tag check fault occurs.
In asynchronous mode, if a tag check fault occurs, the TFSR_EL1 register is
updated asynchronously. The kernel checks the corresponding bits
periodically.

KASAN requires a specific kernel command line parameter to make use of this
hw features.

Add KASAN HW execution mode kernel command line parameter.

Note: This patch adds the kasan.mode kernel parameter and the
sync/async kernel command line options to enable the described features.

Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino's avatarVincenzo Frascino <vincenzo.frascino@arm.com>
[ Add a new var instead of exposing kasan_arg_mode to be consistent with
  flags for other command line arguments. ]
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
parent 6c4e0198
......@@ -161,6 +161,15 @@ particular KASAN features.
- ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
- ``kasan.mode=sync`` or ``=async`` controls whether KASAN is configured in
synchronous or asynchronous mode of execution (default: ``sync``).
Synchronous mode: a bad access is detected immediately when a tag
check fault occurs.
Asynchronous mode: a bad access detection is delayed. When a tag check
fault occurs, the information is stored in hardware (in the TFSR_EL1
register for arm64). The kernel periodically checks the hardware and
only reports tag faults during these checks.
- ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
traces collection (default: ``on``).
......
......@@ -97,7 +97,7 @@ static void kasan_test_exit(struct kunit *test)
READ_ONCE(fail_data.report_found)); \
if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) { \
if (READ_ONCE(fail_data.report_found)) \
hw_enable_tagging(); \
hw_enable_tagging_sync(); \
migrate_enable(); \
} \
} while (0)
......
......@@ -25,6 +25,12 @@ enum kasan_arg {
KASAN_ARG_ON,
};
enum kasan_arg_mode {
KASAN_ARG_MODE_DEFAULT,
KASAN_ARG_MODE_SYNC,
KASAN_ARG_MODE_ASYNC,
};
enum kasan_arg_stacktrace {
KASAN_ARG_STACKTRACE_DEFAULT,
KASAN_ARG_STACKTRACE_OFF,
......@@ -38,6 +44,7 @@ enum kasan_arg_fault {
};
static enum kasan_arg kasan_arg __ro_after_init;
static enum kasan_arg_mode kasan_arg_mode __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;
......@@ -45,6 +52,10 @@ static enum kasan_arg_fault kasan_arg_fault __ro_after_init;
DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
EXPORT_SYMBOL(kasan_flag_enabled);
/* Whether the asynchronous mode is enabled. */
bool kasan_flag_async __ro_after_init;
EXPORT_SYMBOL_GPL(kasan_flag_async);
/* Whether to collect alloc/free stack traces. */
DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
......@@ -68,6 +79,21 @@ static int __init early_kasan_flag(char *arg)
}
early_param("kasan", early_kasan_flag);
/* kasan.mode=sync/async */
static int __init early_kasan_mode(char *arg)
{
/* If arg is not set the default mode is sync */
if ((!arg) || !strcmp(arg, "sync"))
kasan_arg_mode = KASAN_ARG_MODE_SYNC;
else if (!strcmp(arg, "async"))
kasan_arg_mode = KASAN_ARG_MODE_ASYNC;
else
return -EINVAL;
return 0;
}
early_param("kasan.mode", early_kasan_mode);
/* kasan.stacktrace=off/on */
static int __init early_kasan_flag_stacktrace(char *arg)
{
......@@ -115,7 +141,15 @@ void kasan_init_hw_tags_cpu(void)
return;
hw_init_tags(KASAN_TAG_MAX);
hw_enable_tagging();
/*
* Enable async mode only when explicitly requested through
* the command line.
*/
if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
hw_enable_tagging_async();
else
hw_enable_tagging_sync();
}
/* kasan_init_hw_tags() is called once on boot CPU. */
......@@ -132,6 +166,22 @@ void __init kasan_init_hw_tags(void)
/* Enable KASAN. */
static_branch_enable(&kasan_flag_enabled);
switch (kasan_arg_mode) {
case KASAN_ARG_MODE_DEFAULT:
/*
* Default to sync mode.
* Do nothing, kasan_flag_async keeps its default value.
*/
break;
case KASAN_ARG_MODE_SYNC:
/* Do nothing, kasan_flag_async keeps its default value. */
break;
case KASAN_ARG_MODE_ASYNC:
/* Async mode enabled. */
kasan_flag_async = true;
break;
}
switch (kasan_arg_stacktrace) {
case KASAN_ARG_STACKTRACE_DEFAULT:
/* Default to enabling stack trace collection. */
......
......@@ -21,6 +21,7 @@ static inline bool kasan_stack_collection_enabled(void)
#endif
extern bool kasan_flag_panic __ro_after_init;
extern bool kasan_flag_async __ro_after_init;
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
#define KASAN_GRANULE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
......@@ -294,7 +295,8 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
#define arch_set_mem_tag_range(addr, size, tag) ((void *)(addr))
#endif
#define hw_enable_tagging() arch_enable_tagging()
#define hw_enable_tagging_sync() arch_enable_tagging_sync()
#define hw_enable_tagging_async() arch_enable_tagging_async()
#define hw_init_tags(max_tag) arch_init_tags(max_tag)
#define hw_set_tagging_report_once(state) arch_set_tagging_report_once(state)
#define hw_get_random_tag() arch_get_random_tag()
......@@ -303,7 +305,8 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
#else /* CONFIG_KASAN_HW_TAGS */
#define hw_enable_tagging()
#define hw_enable_tagging_sync()
#define hw_enable_tagging_async()
#define hw_set_tagging_report_once(state)
#endif /* CONFIG_KASAN_HW_TAGS */
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment