Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756088AbcL0Can (ORCPT ); Mon, 26 Dec 2016 21:30:43 -0500 Received: from mail-wj0-f194.google.com ([209.85.210.194]:36505 "EHLO mail-wj0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753558AbcL0Cak (ORCPT ); Mon, 26 Dec 2016 21:30:40 -0500 Date: Tue, 27 Dec 2016 05:24:05 +0300 From: "Kirill A. Shutemov" To: Andy Lutomirski Cc: "Kirill A. Shutemov" , 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 Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR Message-ID: <20161227022405.GA8780@node.shutemov.name> References: <20161227015413.187403-1-kirill.shutemov@linux.intel.com> <20161227015413.187403-30-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2600 Lines: 61 On Mon, Dec 26, 2016 at 06:06:01PM -0800, Andy Lutomirski wrote: > 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. My plan was to implement ELF flag on top. Basically, ELF flag would mean that we bump soft limit to hard limit on exec. > That way setuid works right. Um.. I probably miss background here. -- Kirill A. Shutemov