linux-kernel - Re: [PATCH v2 1/4] kasan, arm64: Add KASAN light mode

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Message-ID: <20210113171602.GD27045@gaia>
Date:   Wed, 13 Jan 2021 17:16:02 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, Will Deacon <will@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v2 1/4] kasan, arm64: Add KASAN light mode

On Thu, Jan 07, 2021 at 05:29:05PM +0000, Vincenzo Frascino wrote:
> Architectures supported by KASAN HW can provide a light mode of
> execution. On an MTE enabled arm64 hw for example this can be identified
> with the asynch mode of execution. If an async exception occurs, the
> arm64 core updates a register which is asynchronously detected the next
> time in which the kernel is accessed.

What do you mean by "the kernel is accessed"? Also, there is no
"exception" as such, only a bit in a register updated asynchronously. So
the last sentence could be something like:

  In this mode, if a tag check fault occurs, the TFSR_EL1 register is
  updated asynchronously. The kernel checks the corresponding bits
  periodically.

(or you can be more precise on when the kernel checks for such faults)

> KASAN requires a specific mode of execution to make use of this hw feature.
> 
> Add KASAN HW light execution mode.

Shall we call it "fast"? ;)

> --- /dev/null
> +++ b/include/linux/kasan_def.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_KASAN_DEF_H
> +#define _LINUX_KASAN_DEF_H
> +
> +enum kasan_arg_mode {
> +	KASAN_ARG_MODE_DEFAULT,
> +	KASAN_ARG_MODE_OFF,
> +	KASAN_ARG_MODE_LIGHT,
> +	KASAN_ARG_MODE_PROD,
> +	KASAN_ARG_MODE_FULL,
> +};
> +
> +enum kasan_arg_stacktrace {
> +	KASAN_ARG_STACKTRACE_DEFAULT,
> +	KASAN_ARG_STACKTRACE_OFF,
> +	KASAN_ARG_STACKTRACE_ON,
> +};
> +
> +enum kasan_arg_fault {
> +	KASAN_ARG_FAULT_DEFAULT,
> +	KASAN_ARG_FAULT_REPORT,
> +	KASAN_ARG_FAULT_PANIC,
> +};
> +
> +#endif /* _LINUX_KASAN_DEF_H */

I thought we agreed not to expose the KASAN internal but come up with
another abstraction. Maybe this was after you posted these patches.

-- 
Catalin