linux-kernel - Re: [RFC PATCH 7/8] arm64/mm: Use reduced VA sizes (36/39/42 bits) only for user space

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <861pzx3gll.wl-maz@kernel.org>
Date: Wed, 30 Oct 2024 12:44:38 +0000
From: Marc Zyngier <maz@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Ryan Roberts <ryan.roberts@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH 7/8] arm64/mm: Use reduced VA sizes (36/39/42 bits) only for user space

On Wed, 30 Oct 2024 10:18:11 +0000,
Ard Biesheuvel <ardb+git@...gle.com> wrote:
> 
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> The advantage of a reduced virtual address space size is its impact on
> the number of translation levels, which affects TLB pressure. The
> working set of translations covering the kernel side is negligible
> compared to user space, where each process has its own set of page
> tables, and so most of the same benefit can be obtained by reducing the
> VA size only for user space.
> 
> As a preparatory step towards implementing this, drop all the reduced VA
> space sizes in Kconfig, and replace it with a configurable userland VA
> space size that is reflected in TASK_SIZE. This will be taken advantage
> of in a subsequent patch to actually reduce the number of translations
> used by the MMU for translating user space virtual addresses.

I think this may have an impact on KVM's walking of the userspace page
tables to determine whether we are trying to install a block mapping,
which assumes that the start level and the number of VA bits are the
same as the kernel (see get_user_mapping_size()).

Probably nothing too complicated, but something to look into.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.