Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756288AbcL0DW1 (ORCPT ); Mon, 26 Dec 2016 22:22:27 -0500 Received: from mail-ua0-f171.google.com ([209.85.217.171]:35046 "EHLO mail-ua0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756245AbcL0DWZ (ORCPT ); Mon, 26 Dec 2016 22:22:25 -0500 MIME-Version: 1.0 In-Reply-To: <20161227022405.GA8780@node.shutemov.name> References: <20161227015413.187403-1-kirill.shutemov@linux.intel.com> <20161227015413.187403-30-kirill.shutemov@linux.intel.com> <20161227022405.GA8780@node.shutemov.name> From: Andy Lutomirski Date: Mon, 26 Dec 2016 19:22:03 -0800 Message-ID: Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR To: "Kirill A. Shutemov" 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 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 uBR3MZSG012624 Content-Length: 2971 Lines: 68 On Mon, Dec 26, 2016 at 6:24 PM, Kirill A. Shutemov wrote: > 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. > If a setuid program depends on the lower limit, then a malicious program shouldn't be able to cause it to run with the higher limit. The personality code should already get this case right because personalities are reset when setuid happens. --Andy