[PATCH v2 2/9] kasan: sw_tags: Check kasan_flag_enabled at runtime

Samuel Holland
2024-10-22T02:04:30Z

On RISC-V, the ISA extension required to dereference tagged pointers is
optional, and the interface to enable pointer masking requires firmware
support. Therefore, we must detect at runtime if sw_tags is usable on a
given machine. Reuse the logic from hw_tags to dynamically enable KASAN.

This commit makes no functional change to the KASAN_HW_TAGS code path.

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v1)

include/linux/kasan-enabled.h | 15 +++++----------
mm/kasan/hw_tags.c | 10 ----------
mm/kasan/tags.c | 10 ++++++++++
3 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
index 6f612d69ea0c..648bda9495b7 100644
--- a/include/linux/kasan-enabled.h
+++ b/include/linux/kasan-enabled.h
@@ -4,7 +4,7 @@

#include <linux/static_key.h>

-#ifdef CONFIG_KASAN_HW_TAGS
+#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)

DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);

@@ -13,23 +13,18 @@ static __always_inline bool kasan_enabled(void)
return static_branch_likely(&kasan_flag_enabled);
}

-static inline bool kasan_hw_tags_enabled(void)
-{
- return kasan_enabled();
-}
-
-#else /* CONFIG_KASAN_HW_TAGS */
+#else /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */

static inline bool kasan_enabled(void)
{
return IS_ENABLED(CONFIG_KASAN);
}

+#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
+
static inline bool kasan_hw_tags_enabled(void)
{
- return false;
+ return IS_ENABLED(CONFIG_KASAN_HW_TAGS) && kasan_enabled();
}

-#endif /* CONFIG_KASAN_HW_TAGS */
-
#endif /* LINUX_KASAN_ENABLED_H */
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 9958ebc15d38..c3beeb94efa5 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -43,13 +43,6 @@ static enum kasan_arg kasan_arg __ro_after_init;
static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;

-/*
- * Whether KASAN is enabled at all.
- * The value remains false until KASAN is initialized by kasan_init_hw_tags().
- */
-DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
-EXPORT_SYMBOL(kasan_flag_enabled);
-
/*
* Whether the selected mode is synchronous, asynchronous, or asymmetric.
* Defaults to KASAN_MODE_SYNC.
@@ -257,9 +250,6 @@ void __init kasan_init_hw_tags(void)

kasan_init_tags();

- /* KASAN is now initialized, enable it. */
- static_branch_enable(&kasan_flag_enabled);
-
pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
kasan_mode_info(),
kasan_vmalloc_enabled() ? "on" : "off",
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index d65d48b85f90..c111d98961ed 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -32,6 +32,13 @@ enum kasan_arg_stacktrace {

static enum kasan_arg_stacktrace kasan_arg_stacktrace __initdata;

+/*
+ * Whether KASAN is enabled at all.
+ * The value remains false until KASAN is initialized by kasan_init_tags().
+ */
+DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
+EXPORT_SYMBOL(kasan_flag_enabled);
+
/* Whether to collect alloc/free stack traces. */
DEFINE_STATIC_KEY_TRUE(kasan_flag_stacktrace);

@@ -92,6 +99,9 @@ void __init kasan_init_tags(void)
if (WARN_ON(!stack_ring.entries))
static_branch_disable(&kasan_flag_stacktrace);
}
+
+ /* KASAN is now initialized, enable it. */
+ static_branch_enable(&kasan_flag_enabled);
}

static void save_stack_info(struct kmem_cache *cache, void *object,
--
2.45.1