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From: Catalin Marinas <catalin.marinas@arm.com>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-arch@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] arm64: compat: Add KUSER_HELPERS config option
Date: Mon, 1 Apr 2019 15:48:56 +0100	[thread overview]
Message-ID: <20190401144855.GJ14874@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190401112025.40807-5-vincenzo.frascino@arm.com>

On Mon, Apr 01, 2019 at 12:20:25PM +0100, Vincenzo Frascino wrote:
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7e34b9eba5de..35c98e91bfeb 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1494,6 +1494,36 @@ config COMPAT
>  
>  	  If you want to execute 32-bit userspace applications, say Y.
>  
> +config KUSER_HELPERS
> +	bool "Enable kuser helpers page for compatibility with 32 bit applications."

I'd say only "Enable kuser helpers page for 32-bit applications" (my
first reading of this sounded like it would be enabled for 64-bit apps
to be on par with 32-bit ones).

> +	depends on COMPAT
> +	default y
> +	help
> +	  Warning: disabling this option may break user programs.

"may break 32-bit user programs."

> +
> +	  Provide kuser helpers to compat tasks. The kernel provides
> +	  helper code to userspace in read only form at a fixed location
> +	  to allow userspace to be independent of the CPU type fitted to
> +	  the system. This permits binaries to be run on ARMv4 through
> +	  to ARMv8 without modification.
> +
> +	  See Documentation/arm/kernel_user_helpers.txt for details.
> +
> +	  However, the fixed address nature of these helpers can be used
> +	  by ROP (return orientated programming) authors when creating
> +	  exploits.
> +
> +	  If all of the binaries and libraries which run on your platform
> +	  are built specifically for your platform, and make no use of
> +	  these helpers, then you can turn this option off to hinder
> +	  such exploits. However, in that case, if a binary or library
> +	  relying on those helpers is run, it will not function correctly.
> +
> +	  Note: kuser helpers is disabled by default with 64K pages.

Is it?

> +
> +	  Say N here only if you are absolutely certain that you do not
> +	  need these helpers; otherwise, the safe option is to say Y.
> +

-- 
Catalin

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  reply	other threads:[~2019-04-01 14:49 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-01 11:20 [PATCH 0/4] arm64: compat: Add kuser helpers config option Vincenzo Frascino
2019-04-01 11:20 ` [PATCH 1/4] arm64: compat: Alloc separate pages for vectors and sigpage Vincenzo Frascino
2019-04-01 14:27   ` Catalin Marinas
2019-04-02 10:01     ` Vincenzo Frascino
2019-04-02 10:06       ` Catalin Marinas
2019-04-02 10:08         ` Vincenzo Frascino
2019-04-01 11:20 ` [PATCH 2/4] arm64: compat: Split kuser32 Vincenzo Frascino
2019-04-01 14:30   ` Catalin Marinas
2019-04-02  9:47     ` Vincenzo Frascino
2019-04-01 11:20 ` [PATCH 3/4] arm64: compat: Refactor aarch32_alloc_vdso_pages() Vincenzo Frascino
2019-04-01 14:43   ` Catalin Marinas
2019-04-02 10:06     ` Vincenzo Frascino
2019-04-01 11:20 ` [PATCH 4/4] arm64: compat: Add KUSER_HELPERS config option Vincenzo Frascino
2019-04-01 14:48   ` Catalin Marinas [this message]
2019-04-02 10:12     ` Vincenzo Frascino

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