Subject: Re: [PATCH v2 10/19] arm64: mte: Handle synchronous and asynchronous tag check faults

From: Catalin Marinas <[email-masked]>
Date: Thu, 27 Feb 2020 11:50:31 +0000

On Wed, Feb 26, 2020 at 06:05:17PM +0000, Catalin Marinas wrote:
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index fc6488660f64..d4a378bc0a60 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE)		+= crash_core.o
>  obj-$(CONFIG_ARM_SDE_INTERFACE)		+= sdei.o
>  obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
>  obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o
> +obj-$(CONFIG_ARM64_MTE)			+= mte.o
>  
>  obj-y					+= vdso/ probes/
>  obj-$(CONFIG_COMPAT_VDSO)		+= vdso32/
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 9461d812ae27..9338b340e869 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
[...]
> @@ -738,6 +763,8 @@ work_pending:
>   */
>  ret_to_user:
>  	disable_daif
> +	/* Check for asynchronous tag check faults in the uaccess routines */
> +	check_mte_async_tcf x1, x2
>  	gic_prio_kentry_setup tmp=x3
>  	ldr	x1, [tsk, #TSK_TI_FLAGS]
>  	and	x2, x1, #_TIF_WORK_MASK

I got this wrong, check_mte_async expects the flags as the first
argument (one may experience weird behaviour with overriding the TIF
flags; thanks to Kevin for debugging). The diff below should fix it:

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 9338b340e869..6e7f315911e8 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -764,9 +764,9 @@ work_pending:
 ret_to_user:
 	disable_daif
 	/* Check for asynchronous tag check faults in the uaccess routines */
-	check_mte_async_tcf x1, x2
 	gic_prio_kentry_setup tmp=x3
 	ldr	x1, [tsk, #TSK_TI_FLAGS]
+	check_mte_async_tcf x1, x2
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
 finish_ret_to_user:

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