Re: [PATCH 05/11] kasan, arm64: allow using KUnit tests with HW_TAGS mode

From: Catalin Marinas <catalin.marinas@arm.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	Marco Elver <elver@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will.deacon@arm.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Branislav Rankov <Branislav.Rankov@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 05/11] kasan, arm64: allow using KUnit tests with HW_TAGS mode
Date: Tue, 12 Jan 2021 19:01:32 +0000	[thread overview]
Message-ID: <X/3yDGfTJ+ng+GJt@Catalins-MacBook-Air.local> (raw)
In-Reply-To: <dd061dfca76dbf86af13393edacd37e0c75b6f4a.1609871239.git.andreyknvl@google.com>

On Tue, Jan 05, 2021 at 07:27:49PM +0100, Andrey Konovalov wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..57d3f165d907 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -302,12 +302,20 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
>  static void report_tag_fault(unsigned long addr, unsigned int esr,
>  			     struct pt_regs *regs)
>  {
> -	bool is_write  = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> +	static bool reported;
> +	bool is_write;
> +
> +	if (READ_ONCE(reported))
> +		return;
> +
> +	if (mte_report_once())
> +		WRITE_ONCE(reported, true);

I guess the assumption here is that you don't get any report before the
tests start and temporarily set report_once to false. It's probably
fine, if we get a tag check failure we'd notice in the logs anyway.

>  	/*
>  	 * SAS bits aren't set for all faults reported in EL1, so we can't
>  	 * find out access size.
>  	 */
> +	is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;

I now noticed, you could write this in a shorter way:

	is_write = !!(esr & ESR_ELx_WNR);

>  	kasan_report(addr, 0, is_write, regs->pc);
>  }

The patch looks fine to me.

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