From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Catalin Marinas <catalin.marinas@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: Tue, 2 Apr 2019 11:12:37 +0100 [thread overview]
Message-ID: <4a56f2ed-9325-a6c1-7005-9e7e64a787fe@arm.com> (raw)
In-Reply-To: <20190401144855.GJ14874@arrakis.emea.arm.com>
On 01/04/2019 15:48, Catalin Marinas wrote:
> 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).
>
Ok, I agree, it can be misleading.
>> + depends on COMPAT
>> + default y
>> + help
>> + Warning: disabling this option may break user programs.
>
> "may break 32-bit user programs."
>
Ok.
>> +
>> + 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?
>
Oops... I removed it from all the places except here. Will fix in v2.
>> +
>> + Say N here only if you are absolutely certain that you do not
>> + need these helpers; otherwise, the safe option is to say Y.
>> +
>
--
Regards,
Vincenzo
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prev parent reply other threads:[~2019-04-02 10:12 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
2019-04-02 10:12 ` Vincenzo Frascino [this message]
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