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.

[ Add a new var instead of exposing kasan_arg_mode to be consistent with
  flags for other command line arguments. ]

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: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/20210315132019.33202-3-vincenzo.frascino@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index ddf4239a58908cef17c30b716d86277bd49911c4..6f6ab3ed7b793aecc569b96128c7ab34c8e8a753 100644 (file)
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -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``).
 

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index e5647d147b35059d4cb06f41c375fb62b37ea14e..479c31a5dc214b8cd895f4cb5b1cef0a99d734c1 100644 (file)
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -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))          \
-                       kasan_enable_tagging();                 \
+                       kasan_enable_tagging_sync();            \
                migrate_enable();                               \
        }                                                       \
 } while (0)

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 2aad21fda156e4d79e5198a856b1e5da293de46f..1df4ce803861427a70c80031521cc0fb5e163dcb 100644 (file)
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -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 +79,23 @@ 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)
+               return -EINVAL;
+
+       if (!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 +143,15 @@ 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 +168,22 @@ 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. */
@@ -194,10 +246,10 @@ void kasan_set_tagging_report_once(bool state)
 }
 EXPORT_SYMBOL_GPL(kasan_set_tagging_report_once);
 
-void kasan_enable_tagging(void)
+void kasan_enable_tagging_sync(void)
 {
-       hw_enable_tagging();
+       hw_enable_tagging_sync();
 }
-EXPORT_SYMBOL_GPL(kasan_enable_tagging);
+EXPORT_SYMBOL_GPL(kasan_enable_tagging_sync);
 
 #endif

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 8c55634d6edd92fbab6d0c7030b819364d3f1ced..a3d0d165d97d1f4376067247cf1ba81f9aeffe1a 100644 (file)
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -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)
@@ -275,8 +276,11 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
 
 #ifdef CONFIG_KASAN_HW_TAGS
 
-#ifndef arch_enable_tagging
-#define arch_enable_tagging()
+#ifndef arch_enable_tagging_sync
+#define arch_enable_tagging_sync()
+#endif
+#ifndef arch_enable_tagging_async
+#define arch_enable_tagging_async()
 #endif
 #ifndef arch_init_tags
 #define arch_init_tags(max_tag)
@@ -294,7 +298,8 @@ 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 +308,8 @@ 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 */
@@ -311,12 +317,12 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
 #if defined(CONFIG_KASAN_HW_TAGS) && IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 
 void kasan_set_tagging_report_once(bool state);
-void kasan_enable_tagging(void);
+void kasan_enable_tagging_sync(void);
 
 #else /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */
 
 static inline void kasan_set_tagging_report_once(bool state) { }
-static inline void kasan_enable_tagging(void) { }
+static inline void kasan_enable_tagging_sync(void) { }
 
 #endif /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */