linux-kernel - Re: [PATCH 1/3] arm64: adjust el0_sync so that a function can be called

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Message-ID: <20140429094211.GC17007@arm.com>
Date:	Tue, 29 Apr 2014 10:42:11 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Larry Bassel <larry.bassel@...aro.org>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"khilman@...aro.org" <khilman@...aro.org>
Subject: Re: [PATCH 1/3] arm64: adjust el0_sync so that a function can be
 called

On Sun, Apr 27, 2014 at 08:44:12PM +0100, Larry Bassel wrote:
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 39ac630..eda7755 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
[...]
> @@ -421,28 +421,30 @@ el0_da:
>  	/*
>  	 * Data abort handling
>  	 */
> -	mrs	x0, far_el1
> -	bic	x0, x0, #(0xff << 56)
>  	disable_step x1
>  	isb
>  	enable_dbg
>  	// enable interrupts before calling the main handler
>  	enable_irq
> +	mrs	x0, far_el1
> +	bic	x0, x0, #(0xff << 56)
>  	mov	x1, x25
>  	mov	x2, sp
> +	adr	lr, ret_from_exception
>  	b	do_mem_abort

Reading the far_el1 after enable_dbg and enable_irq is racy, we can no
longer guarantee its value in the original data abort context.

>  el0_ia:
>  	/*
>  	 * Instruction abort handling
>  	 */
> -	mrs	x0, far_el1
>  	disable_step x1
>  	isb
>  	enable_dbg
>  	// enable interrupts before calling the main handler
>  	enable_irq
> +	mrs	x0, far_el1
>  	orr	x1, x25, #1 << 24		// use reserved ISS bit for instruction aborts
>  	mov	x2, sp
> +	adr	lr, ret_from_exception
>  	b	do_mem_abort
>  el0_fpsimd_acc:

Same here.

-- 
Catalin
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