On Tue, Sep 08, 2020 at 03:18:04PM +0200, Andrey Konovalov wrote:

On Thu, Aug 27, 2020 at 12:40 PM Catalin Marinas
[off-list ref] wrote:

quoted

On Fri, Aug 14, 2020 at 07:27:08PM +0200, Andrey Konovalov wrote:

quoted

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 152d74f2cc9c..6880ddaa5144 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S

@@ -38,7 +38,7 @@
 /* PTWs cacheable, inner/outer WBWA */
 #define TCR_CACHE_FLAGS      TCR_IRGN_WBWA | TCR_ORGN_WBWA

-#ifdef CONFIG_KASAN_SW_TAGS
+#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
 #define TCR_KASAN_FLAGS TCR_TBI1
 #else
 #define TCR_KASAN_FLAGS 0

I prefer to turn TBI1 on only if MTE is present. So on top of the v8
user series, just do this in __cpu_setup.

Started working on this, but realized that I don't understand what
exactly is suggested here. TCR_KASAN_FLAGS are used in __cpu_setup(),
so this already happens in __cpu_setup().

Do you mean that TBI1 should be enabled when CONFIG_ARM64_MTE is
enabled, but CONFIG_KASAN_HW_TAGS is disabled?

What I meant is that we should turn TBI1 only when the MTE is present in
hardware (and the ARM64_MTE option is on). But I probably missed the way
MTE is used with KASAN.

So what happens if CONFIG_KASAN_HW_TAGS and CONFIG_ARM64_MTE are both on
but the hardware does not support MTE? Does KASAN still generate tagged
pointers? If yes, then the current patch is fine, we should always set
TBI1.

-- 
Catalin

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