Re: [PATCH v15 5/8] arm64: mte: Enable TCO in functions that can read beyond buffer limits

On 3/12/21 3:13 PM, Catalin Marinas wrote:

On Fri, Mar 12, 2021 at 02:22:07PM +0000, Vincenzo Frascino wrote:

quoted

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 9b557a457f24..8603c6636a7d 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h

@@ -90,5 +90,20 @@ static inline void mte_assign_mem_tag_range(void *addr, size_t size)
 
 #endif /* CONFIG_ARM64_MTE */
 
+#ifdef CONFIG_KASAN_HW_TAGS
+/* Whether the MTE asynchronous mode is enabled. */
+DECLARE_STATIC_KEY_FALSE(mte_async_mode);
+
+static inline bool system_uses_mte_async_mode(void)
+{
+	return static_branch_unlikely(&mte_async_mode);
+}
+#else
+static inline bool system_uses_mte_async_mode(void)
+{
+	return false;
+}
+#endif /* CONFIG_KASAN_HW_TAGS */

You can write this with fewer lines:

DECLARE_STATIC_KEY_FALSE(mte_async_mode);

static inline bool system_uses_mte_async_mode(void)
{
	return IS_ENABLED(CONFIG_KASAN_HW_TAGS) &&
		static_branch_unlikely(&mte_async_mode);
}

The compiler will ensure that mte_async_mode is not referred when
!CONFIG_KASAN_HW_TAGS and therefore doesn't need to be defined.

Yes, I agree, but I introduce "#ifdef CONFIG_KASAN_HW_TAGS" in the successive
patch anyway, according to me the overall code looks more uniform like this. But
I do not have a strong opinion or preference on this.

quoted

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index fa755cf94e01..9362928ba0d5 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -26,6 +26,10 @@ u64 gcr_kernel_excl __ro_after_init;
 
 static bool report_fault_once = true;
 
+/* Whether the MTE asynchronous mode is enabled. */
+DEFINE_STATIC_KEY_FALSE(mte_async_mode);
+EXPORT_SYMBOL_GPL(mte_async_mode);

Maybe keep these bracketed by #ifdef CONFIG_KASAN_HW_TAGS. I think the
mte_enable_kernel_*() aren't needed either if KASAN_HW is disabled (you
can do it with an additional patch).

Makes sense, I will add it in the next version.

With these, you can add:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

-- 
Regards,
Vincenzo

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