Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755903AbcL0COB (ORCPT ); Mon, 26 Dec 2016 21:14:01 -0500 Received: from mail-vk0-f54.google.com ([209.85.213.54]:33250 "EHLO mail-vk0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754496AbcL0COA (ORCPT ); Mon, 26 Dec 2016 21:14:00 -0500 MIME-Version: 1.0 In-Reply-To: <20161227015413.187403-30-kirill.shutemov@linux.intel.com> References: <20161227015413.187403-1-kirill.shutemov@linux.intel.com> <20161227015413.187403-30-kirill.shutemov@linux.intel.com> From: Andy Lutomirski Date: Mon, 26 Dec 2016 18:06:01 -0800 Message-ID: Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR To: "Kirill A. Shutemov" Cc: Linus Torvalds , Andrew Morton , X86 ML , Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" , Andi Kleen , Dave Hansen , linux-arch , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Linux API Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id uBR2E5KD030057 Content-Length: 2248 Lines: 50 On Mon, Dec 26, 2016 at 5:54 PM, Kirill A. Shutemov wrote: > This patch introduces new rlimit resource to manage maximum virtual > address available to userspace to map. > > On x86, 5-level paging enables 56-bit userspace virtual address space. > Not all user space is ready to handle wide addresses. It's known that > at least some JIT compilers use high bit in pointers to encode their > information. It collides with valid pointers with 5-level paging and > leads to crashes. > > The patch aims to address this compatibility issue. > > MM would use min(RLIMIT_VADDR, TASK_SIZE) as upper limit of virtual > address available to map by userspace. > > The default hard limit will be RLIM_INFINITY, which basically means that > TASK_SIZE limits available address space. > > The soft limit will also be RLIM_INFINITY everywhere, but the machine > with 5-level paging enabled. In this case, soft limit would be > (1UL << 47) - PAGE_SIZE. It’s current x86-64 TASK_SIZE_MAX with 4-level > paging which known to be safe > > New rlimit resource would follow usual semantics with regards to > inheritance: preserved on fork(2) and exec(2). This has potential to > break application if limits set too wide or too narrow, but this is not > uncommon for other resources (consider RLIMIT_DATA or RLIMIT_AS). > > As with other resources you can set the limit lower than current usage. > It would affect only future virtual address space allocations. > > Use-cases for new rlimit: > > - Bumping the soft limit to RLIM_INFINITY, allows current process all > its children to use addresses above 47-bits. > > - Bumping the soft limit to RLIM_INFINITY after fork(2), but before > exec(2) allows the child to use addresses above 47-bits. > > - Lowering the hard limit to 47-bits would prevent current process all > its children to use addresses above 47-bits, unless a process has > CAP_SYS_RESOURCES. > > - It’s also can be handy to lower hard or soft limit to arbitrary > address. User-mode emulation in QEMU may lower the limit to 32-bit > to emulate 32-bit machine on 64-bit host. I tend to think that this should be a personality or an ELF flag, not an rlimit. That way setuid works right.