From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f197.google.com (mail-io0-f197.google.com [209.85.223.197]) by kanga.kvack.org (Postfix) with ESMTP id 7D4A86B0033 for ; Thu, 12 Jan 2017 20:32:22 -0500 (EST) Received: by mail-io0-f197.google.com with SMTP id v96so47178197ioi.5 for ; Thu, 12 Jan 2017 17:32:22 -0800 (PST) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id p23si10976303pfl.37.2017.01.12.17.32.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Jan 2017 17:32:21 -0800 (PST) Subject: Re: [PATCH v4 0/4] Application Data Integrity feature introduced by SPARC M7 References: <621cfed0-3e56-13e6-689a-0637bce164fe@linux.intel.com> <11d20dac-2c0f-6e9a-7f98-3839c749adb6@linux.intel.com> <4978715f-e5e8-824e-3804-597eaa0beb95@oracle.com> <558ad70b-4b19-3a78-038a-b12dc7af8585@linux.intel.com> <5d28f71e-1ad2-b2f9-1174-ea4eb6399d23@oracle.com> From: Rob Gardner Message-ID: Date: Thu, 12 Jan 2017 18:31:45 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Khalid Aziz , Dave Hansen , davem@davemloft.net, corbet@lwn.net, arnd@arndb.de, akpm@linux-foundation.org Cc: hpa@zytor.com, viro@zeniv.linux.org.uk, nitin.m.gupta@oracle.com, chris.hyser@oracle.com, tushar.n.dave@oracle.com, sowmini.varadhan@oracle.com, mike.kravetz@oracle.com, adam.buchbinder@gmail.com, minchan@kernel.org, hughd@google.com, kirill.shutemov@linux.intel.com, keescook@chromium.org, allen.pais@oracle.com, aryabinin@virtuozzo.com, atish.patra@oracle.com, joe@perches.com, pmladek@suse.com, jslaby@suse.cz, cmetcalf@mellanox.com, paul.gortmaker@windriver.com, mhocko@suse.com, jmarchan@redhat.com, lstoakes@gmail.com, 0x7f454c46@gmail.com, vbabka@suse.cz, tglx@linutronix.de, mingo@redhat.com, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net, vdavydov.dev@gmail.com, hannes@cmpxchg.org, namit@vmware.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org On 01/12/2017 05:22 PM, Khalid Aziz wrote: > On 01/12/2017 10:53 AM, Dave Hansen wrote: >> On 01/12/2017 08:50 AM, Khalid Aziz wrote: >>> 2. Any shared page that has ADI protection enabled on it, must stay ADI >>> protected across all processes sharing it. >> >> Is that true? >> >> What happens if a page with ADI tags set is accessed via a PTE without >> the ADI enablement bit set? > > ADI protection applies across all processes in terms of all of them > must use the same tag to access the shared memory, but if a process > accesses a shared page with TTE.mcde bit cleared, access will be granted. > >> >>> COW creates an intersection of the two. It creates a new copy of the >>> shared data. It is a new data page and hence the process creating it >>> must be the one responsible for enabling ADI protection on it. >> >> Do you mean that the application must be responsible? Or the kernel >> running in the context of the new process must be responsible? >> >>> It is also a copy of what was ADI protected data, so should it >>> inherit the protection instead? >> >> I think the COW'd copy must inherit the VMA bit, the PTE bits, and the >> tags on the cachelines. >> >>> I misspoke earlier. I had misinterpreted the results of test I ran. >>> Changing the tag on shared memory is allowed by memory controller. The >>> requirement is every one sharing the page must switch to the new tag or >>> else they get SIGSEGV. >> >> I asked this in the last mail, but I guess I'll ask it again. Please >> answer this directly. >> >> If we require that everyone coordinate their tags on the backing >> physical memory, and we allow a lower-privileged program to access the >> same data as a more-privileged one, then the lower-privilege app can >> cause arbitrary crashes in the privileged application. >> >> For instance, say sudo mmap()'s /etc/passwd and uses ADI tags to protect >> the mapping. Couldn't any other app in the system prevent sudo from >> working? >> >> How can we *EVER* allow tags to be set on non-writable mappings? I don't think you can write a tag to memory if you don't have write access in the TTE. Writing a tag requires a store instruction, and if the machine is at all sane, this will fault if you don't have write access. Rob > > I understand your quetion better now. That is a very valid concern. > Using ADI tags to prevent an unauthorized process from just reading > data in memory, say an in-memory copy of database, is one of the use > cases for ADI. This means there is a reasonable case to allow enabling > ADI and setting tags even on non-writable mappings. On the other hand, > if an unauthorized process manages to map the right memory pages in > its address space, it can read them any way by not setting TTE.mcd. > > Userspace app can set tag on any memory it has mapped in without > requiring assistance from kernel. Can this problem be solved by not > allowing setting TTE.mcd on non-writable mappings? Doesn't the same > problem occur on writable mappings? If a privileged process mmap()'s a > writable file with MAP_SHARED, enables ADI and sets tag on the mmap'd > memory region, then another lower privilege process mmap's the same > file writable (assuming file permissions allow it to), enables ADI and > sets a different tag on it, the privileged process would get SIGSEGV > when it tries to access the mmap'd file. Right? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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