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,
Jann Horn <jannh@google.com>
Subject: Re: [PATCH 4/5] arm64: compat: Add KUSER_HELPERS config option
Date: Fri, 29 Mar 2019 12:22:16 +0000 [thread overview]
Message-ID: <20190329122216.xa6va62qwyynoldt@mbp> (raw)
In-Reply-To: <20190319151542.19557-5-vincenzo.frascino@arm.com>
On Tue, Mar 19, 2019 at 03:15:41PM +0000, Vincenzo Frascino wrote:
> When kuser helpers are enabled the kernel maps the relative code at
> a fixed address (0xffff0000). Making configurable the option to disable
> them means that the kernel can remove this mapping and any access to
> this memory area results in a sigfault.
>
> Add a KUSER_HELPERS config option that can be used to disable the
> mapping when it is turned off.
>
> This option can be turned off if and only if the applications are
> designed specifically for the platform and they do not make use of the
> kuser helpers code.
>
> Note: kuser helpers is disabled by default with 64K pages.
Actually this last sentence is more than just the default y/n for this
option. It adds a hard dependency, which means it cannot be enabled.
Currently we do allow COMPAT with 64K pages if EXPERT.
Is the main reason for this just to be able to subtract PAGE_SIZE for
TASK_SIZE_32 in the last patch? What happens if we leave TASK_SIZE_32
set to 0x100000000 for the 64K page configuration? Do we still have the
C99 issue mentioned in the cover letter (assuming that the last page is
already occupied by the vectors page)?
--
Catalin
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next prev parent reply other threads:[~2019-03-29 12:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-19 15:15 [PATCH 0/5] arm64: compat: Reduce address limit Vincenzo Frascino
2019-03-19 15:15 ` [PATCH 1/5] arm64: compat: Alloc separate pages for vectors and sigpage Vincenzo Frascino
2019-03-29 12:12 ` Catalin Marinas
2019-04-01 9:00 ` Vincenzo Frascino
2019-03-19 15:15 ` [PATCH 2/5] arm64: compat: Split kuser32 Vincenzo Frascino
2019-03-19 15:15 ` [PATCH 3/5] arm64: compat: Refactor aarch32_alloc_vdso_pages() Vincenzo Frascino
2019-03-19 15:15 ` [PATCH 4/5] arm64: compat: Add KUSER_HELPERS config option Vincenzo Frascino
2019-03-29 12:22 ` Catalin Marinas [this message]
2019-03-19 15:15 ` [PATCH 5/5] arm64: compat: Reduce address limit Vincenzo Frascino
2019-03-29 15:59 ` Catalin Marinas
2019-04-01 9:13 ` Vincenzo Frascino
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