From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-f199.google.com (mail-yw0-f199.google.com [209.85.161.199]) by kanga.kvack.org (Postfix) with ESMTP id 010B46B03AB for ; Tue, 14 Feb 2017 11:15:29 -0500 (EST) Received: by mail-yw0-f199.google.com with SMTP id l19so204339816ywc.5 for ; Tue, 14 Feb 2017 08:15:28 -0800 (PST) Received: from EUR02-AM5-obe.outbound.protection.outlook.com (mail-eopbgr00108.outbound.protection.outlook.com. [40.107.0.108]) by mx.google.com with ESMTPS id h73si906049pfh.1.2017.02.14.08.15.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 14 Feb 2017 08:15:28 -0800 (PST) Subject: Re: [PATCHv4 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) References: <20170130120432.6716-1-dsafonov@virtuozzo.com> <20170130120432.6716-5-dsafonov@virtuozzo.com> From: Dmitry Safonov Message-ID: Date: Tue, 14 Feb 2017 19:11:40 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , x86@kernel.org, linux-mm@kvack.org On 02/11/2017 11:13 PM, Thomas Gleixner wrote: > On Mon, 30 Jan 2017, Dmitry Safonov wrote: > >> At this momet, logic in arch_get_unmapped_area{,_topdown} for mmaps with >> MAP_32BIT flag checks TIF_ADDR32 which means: >> o if 32-bit ELF changes mode to 64-bit on x86_64 and then tries to >> mmap() with MAP_32BIT it'll result in addr over 4Gb (as default is >> top-down allocation) >> o if 64-bit ELF changes mode to 32-bit and tries mmap() with MAP_32BIT, >> it'll allocate only memory in 1GB space: [0x40000000, 0x80000000). >> >> Fix it by handeling MAP_32BIT in 64-bit syscalls only. > > I really have a hard time to understand what is fixed and how that is > related to the $subject. > > Again. Please explain the problem first properly so one can understand the > issue immediately. Ok, rewrote the changes log. > >> As a little bonus it'll make thread flag a little less used. > > I really do not understand the bonus part here. You replace the thread flag > check with a different one and AFAICT this looks like oart of the 'fix'. It's a part of the fix, right. What I meant here is that after those patches TIF_ADDR32 is no more used after exec() time. That's bonus as if we manage to change exec() code in some way (i.e., pass address restriction as a parameter), we'll have additional free thread info flag. > Thanks, > > tglx > >> @@ -101,7 +101,7 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len, >> static void find_start_end(unsigned long flags, unsigned long *begin, >> unsigned long *end) >> { >> - if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) { >> + if (!in_compat_syscall() && (flags & MAP_32BIT)) { >> /* This is usually used needed to map code in small >> model, so it needs to be in the first 31bit. Limit >> it to that. This means we need to move the >> @@ -195,7 +195,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, >> return addr; >> >> /* for MAP_32BIT mappings we force the legacy mmap base */ >> - if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) >> + if (!in_compat_syscall() && (flags & MAP_32BIT)) >> goto bottomup; >> >> /* requesting a specific address */ >> -- >> 2.11.0 >> >> -- Dmitry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org