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Tue, 15 Nov 2022 21:21:11 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 412C8300244; Tue, 15 Nov 2022 22:21:04 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2A30A2C0E2D26; Tue, 15 Nov 2022 22:21:04 +0100 (CET) Date: Tue, 15 Nov 2022 22:21:04 +0100 From: Peter Zijlstra To: Dave Hansen Cc: "Edgecombe, Rick P" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "rdunlap@infradead.org" , "keescook@chromium.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "rppt@linux.ibm.com" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "pavel@ucw.cz" , "arnd@arndb.de" , "tglx@linutronix.de" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "jamorris@linux.microsoft.com" , "rppt@kernel.org" , "john.allen@amd.com" , "mingo@redhat.com" , "Shankar, Ravi V" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" , "akpm@linux-foundation.org" Subject: Re: [PATCH v3 36/37] x86/cet/shstk: Add ARCH_CET_UNLOCK Message-ID: References: <20221104223604.29615-1-rick.p.edgecombe@intel.com> <20221104223604.29615-37-rick.p.edgecombe@intel.com> <4273232513cd178be303d817b15e442703bda637.camel@intel.com> <93029063-4a68-d275-b437-12930e119347@intel.com> MIME-Version: 1.0 Content-Type: text/plain; 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t=1668547279; a=rsa-sha256; cv=none; b=KTvz2qBuQ2Qnsf57ozYyOdCHJHvsTyF42itwSCU8fPjkamvV/3MrSKxZg7cK7Ii9ZgnmV0 X725ABOo/mmfiYq7xE77xKAAc1REJHR2Jvy4uKJ5VgpimCcsn/PO1Yvd1hLYcH6kFJQchL MJP02mnLvSPw5nr0bdOYQPtBqIQuvX0= X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3FF8218000B Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=NwPV9AHg; spf=none (imf16.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none X-Stat-Signature: nrxg347eukthzqqprrd6mdhk5rzqzqxi X-HE-Tag: 1668547278-269370 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Nov 15, 2022 at 01:00:40PM -0800, Dave Hansen wrote: > On 11/15/22 12:57, Peter Zijlstra wrote: > > On Tue, Nov 15, 2022 at 08:01:12PM +0000, Edgecombe, Rick P wrote: > >>>> + if (task != current) { > >>>> + if (option == ARCH_CET_UNLOCK && > >>>> IS_ENABLED(CONFIG_CHECKPOINT_RESTORE)) { > >>> Why make this conditional on CRIU at all? > >> Kees asked for it, I think he was worried about attackers using it to > >> unlock and disable shadow stack. So wanted to lock it down to the > >> maximum. > > Well, distros will all have this stuff enabled no? So not much > > protection in practise. > > Yeah, that's true for the distros. > > But, I would imagine that our more paranoid friends like the ChromeOS > folks might appreciate this. ptrace can modify text, I'm not sure what if anything we're protecting against.