Re: [PATCH v2 02/14] kasan: sw_tags: Check kasan_flag_enabled at runtime
From: Andrey Konovalov <andreyknvl@gmail.com>
Date: 2025-02-19 23:30:23
Also in:
linux-mm, lkml, llvm
On Tue, Feb 18, 2025 at 9:16 AM Maciej Wieczor-Retman [off-list ref] wrote:
From: Samuel Holland <samuel.holland@sifive.com> 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.
Is this patch required on x86 as well? If so, I think it makes sense to point it out here. And do the same in messages for other commits that now mention RISC-V.
quoted hunk ↗ jump to hunk
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> Signed-off-by: Maciej Wieczor-Retman <redacted> --- 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 9a6927394b54..7f82af13b6a6 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c@@ -45,13 +45,6 @@ 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.@@ -259,9 +252,6 @@ 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(), str_on_off(kasan_vmalloc_enabled()),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, --2.47.1