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From: Catalin Marinas <catalin.marinas@arm.com>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>,
	Marco Elver <elver@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	Alexander Potapenko <glider@google.com>,
	linux-arm-kernel@lists.infradead.org,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Will Deacon <will@kernel.org>, Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v2 2/4] arm64: mte: Add asynchronous mode support
Date: Wed, 13 Jan 2021 17:22:28 +0000	[thread overview]
Message-ID: <20210113172228.GE27045@gaia> (raw)
In-Reply-To: <20210107172908.42686-3-vincenzo.frascino@arm.com>

On Thu, Jan 07, 2021 at 05:29:06PM +0000, Vincenzo Frascino wrote:
> MTE provides an asynchronous mode for detecting tag exceptions. In
> particular instead of triggering a fault the arm64 core updates a
> register which is checked by the kernel at the first entry after the tag
> exception has occurred.

Just rephrase the "tag exception" here as there's no exception taken.
Also we don't check this only when the kernel is first entered after a
tag check fault, as per patch 3.

> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -153,8 +153,35 @@ void mte_init_tags(u64 max_tag)
>  
>  void mte_enable_kernel(enum kasan_arg_mode mode)
>  {
> -	/* Enable MTE Sync Mode for EL1. */
> -	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> +	const char *m;
> +
> +	/* Preset parameter values based on the mode. */
> +	switch (mode) {
> +	case KASAN_ARG_MODE_OFF:
> +		return;
> +	case KASAN_ARG_MODE_LIGHT:
> +		/* Enable MTE Async Mode for EL1. */
> +		sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_ASYNC);
> +		m = "asynchronous";
> +		break;
> +	case KASAN_ARG_MODE_DEFAULT:
> +	case KASAN_ARG_MODE_PROD:
> +	case KASAN_ARG_MODE_FULL:
> +		/* Enable MTE Sync Mode for EL1. */
> +		sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> +		m = "synchronous";
> +		break;
> +	default:
> +		/*
> +		 * kasan mode should be always set hence we should
> +		 * not reach this condition.
> +		 */
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

I guess the switch statement here will be re-written as we want kasan to
drive the actual sync/async modes as it sees fit rather than MTE
guessing what PROD/FULL/LIGHT means.

-- 
Catalin

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WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	Will Deacon <will@kernel.org>, Dmitry Vyukov <dvyukov@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Alexander Potapenko <glider@google.com>,
	Marco Elver <elver@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Branislav Rankov <Branislav.Rankov@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH v2 2/4] arm64: mte: Add asynchronous mode support
Date: Wed, 13 Jan 2021 17:22:28 +0000	[thread overview]
Message-ID: <20210113172228.GE27045@gaia> (raw)
In-Reply-To: <20210107172908.42686-3-vincenzo.frascino@arm.com>

On Thu, Jan 07, 2021 at 05:29:06PM +0000, Vincenzo Frascino wrote:
> MTE provides an asynchronous mode for detecting tag exceptions. In
> particular instead of triggering a fault the arm64 core updates a
> register which is checked by the kernel at the first entry after the tag
> exception has occurred.

Just rephrase the "tag exception" here as there's no exception taken.
Also we don't check this only when the kernel is first entered after a
tag check fault, as per patch 3.

> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -153,8 +153,35 @@ void mte_init_tags(u64 max_tag)
>  
>  void mte_enable_kernel(enum kasan_arg_mode mode)
>  {
> -	/* Enable MTE Sync Mode for EL1. */
> -	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> +	const char *m;
> +
> +	/* Preset parameter values based on the mode. */
> +	switch (mode) {
> +	case KASAN_ARG_MODE_OFF:
> +		return;
> +	case KASAN_ARG_MODE_LIGHT:
> +		/* Enable MTE Async Mode for EL1. */
> +		sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_ASYNC);
> +		m = "asynchronous";
> +		break;
> +	case KASAN_ARG_MODE_DEFAULT:
> +	case KASAN_ARG_MODE_PROD:
> +	case KASAN_ARG_MODE_FULL:
> +		/* Enable MTE Sync Mode for EL1. */
> +		sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> +		m = "synchronous";
> +		break;
> +	default:
> +		/*
> +		 * kasan mode should be always set hence we should
> +		 * not reach this condition.
> +		 */
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

I guess the switch statement here will be re-written as we want kasan to
drive the actual sync/async modes as it sees fit rather than MTE
guessing what PROD/FULL/LIGHT means.

-- 
Catalin

  reply	other threads:[~2021-01-13 17:24 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-07 17:29 [PATCH v2 0/4] arm64: ARMv8.5-A: MTE: Add async mode support Vincenzo Frascino
2021-01-07 17:29 ` Vincenzo Frascino
2021-01-07 17:29 ` [PATCH v2 1/4] kasan, arm64: Add KASAN light mode Vincenzo Frascino
2021-01-07 17:29   ` Vincenzo Frascino
2021-01-13 17:16   ` Catalin Marinas
2021-01-13 17:16     ` Catalin Marinas
2021-01-14  9:40     ` Vincenzo Frascino
2021-01-14  9:40       ` Vincenzo Frascino
2021-01-07 17:29 ` [PATCH v2 2/4] arm64: mte: Add asynchronous mode support Vincenzo Frascino
2021-01-07 17:29   ` Vincenzo Frascino
2021-01-13 17:22   ` Catalin Marinas [this message]
2021-01-13 17:22     ` Catalin Marinas
2021-01-14  9:43     ` Vincenzo Frascino
2021-01-14  9:43       ` Vincenzo Frascino
2021-01-07 17:29 ` [PATCH v2 3/4] arm64: mte: Enable async tag check fault Vincenzo Frascino
2021-01-07 17:29   ` Vincenzo Frascino
2021-01-13 18:11   ` Catalin Marinas
2021-01-13 18:11     ` Catalin Marinas
2021-01-14 10:24     ` Vincenzo Frascino
2021-01-14 10:24       ` Vincenzo Frascino
2021-01-14 14:25       ` Catalin Marinas
2021-01-14 14:25         ` Catalin Marinas
2021-01-14 14:57         ` Vincenzo Frascino
2021-01-14 14:57           ` Vincenzo Frascino
2021-01-07 17:29 ` [PATCH v2 4/4] arm64: mte: Optimize mte_assign_mem_tag_range() Vincenzo Frascino
2021-01-07 17:29   ` Vincenzo Frascino

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