Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758470AbdCUVmb convert rfc822-to-8bit (ORCPT ); Tue, 21 Mar 2017 17:42:31 -0400 Received: from terminus.zytor.com ([65.50.211.136]:46344 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758453AbdCUVm3 (ORCPT ); Tue, 21 Mar 2017 17:42:29 -0400 Date: Tue, 21 Mar 2017 14:23:51 -0700 User-Agent: K-9 Mail for Android In-Reply-To: <20170321211648.xcgwigbv37ktxofx@angband.pl> References: <20170321174711.29880-1-dsafonov@virtuozzo.com> <20170321211648.xcgwigbv37ktxofx@angband.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: [PATCHv3] x86/mm: set x32 syscall bit in SET_PERSONALITY() To: Adam Borowski , Dmitry Safonov CC: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, linux-mm@kvack.org, Andrei Vagin , Cyrill Gorcunov , Borislav Petkov , "Kirill A. Shutemov" , x86@kernel.org, Andy Lutomirski , Ingo Molnar , Thomas Gleixner From: hpa@zytor.com Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2260 Lines: 57 On March 21, 2017 2:16:48 PM PDT, Adam Borowski wrote: >On Tue, Mar 21, 2017 at 08:47:11PM +0300, Dmitry Safonov wrote: >> After my changes to mmap(), its code now relies on the bitness of >> performing syscall. According to that, it chooses the base of >allocation: >> mmap_base for 64-bit mmap() and mmap_compat_base for 32-bit syscall. >> It was done by: >> commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for >> 32-bit mmap()"). >> >> The code afterwards relies on in_compat_syscall() returning true for >> 32-bit syscalls. It's usually so while we're in context of >application >> that does 32-bit syscalls. But during exec() it is not valid for x32 >ELF. >> The reason is that the application hasn't yet done any syscall, so >x32 >> bit has not being set. >> That results in -ENOMEM for x32 ELF files as there fired BAD_ADDR() >> in elf_map(), that is called from do_execve()->load_elf_binary(). >> For i386 ELFs it works as SET_PERSONALITY() sets TS_COMPAT flag. >> >> Set x32 bit before first return to userspace, during setting >personality >> at exec(). This way we can rely on in_compat_syscall() during exec(). >> Do also the reverse: drop x32 syscall bit at SET_PERSONALITY for >64-bits. >> >> Fixes: commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for >> 32-bit mmap()") > >Tested: >with bash:x32, mksh:amd64, posh:i386, zsh:armhf (binfmt:qemu), >fork+exec >works for every parent-child combination. > >Contrary to my naive initial reading of your fix, mixing syscalls from >a >process of the wrong ABI also works as it did before. While using a >glibc >wrapper will call the right version, x32 processes calling amd64 >syscalls is >surprisingly common -- this brings seccomp joy. > >I've attached a freestanding test case for write() and mmap(); it's >freestanding asm as most of you don't have an x32 toolchain at hand, >sorry >for unfriendly error messages. > >So with these two patches: >x86/tls: Forcibly set the accessed bit in TLS segments >x86/mm: set x32 syscall bit in SET_PERSONALITY() >everything appears to be fine. What userspace is that? Is this syscall(3) (ab)users or incorrectly ported to x32 software? -- Sent from my Android device with K-9 Mail. Please excuse my brevity.