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Mon, 03 Jul 2023 14:49:30 -0400 X-MC-Unique: P1gDR9jLN9GbuzEdR1I4Vw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DB61F185A791; Mon, 3 Jul 2023 18:49:28 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8AD7DC00049; Mon, 3 Jul 2023 18:49:19 +0000 (UTC) From: Florian Weimer To: szabolcs.nagy@arm.com Cc: "Edgecombe, Rick P" , "Lutomirski, Andy" , "Xu, Pengfei" , "tglx@linutronix.de" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "nadav.amit@gmail.com" , "kirill.shutemov@linux.intel.com" , "david@redhat.com" , "Schimpe, Christina" , "akpm@linux-foundation.org" , "peterz@infradead.org" , "corbet@lwn.net" , "nd@arm.com" , "broonie@kernel.org" , "jannh@google.com" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "debug@rivosinc.com" , "bp@alien8.de" , "rdunlap@infradead.org" , "linux-api@vger.kernel.org" , "rppt@kernel.org" , "jamorris@linux.microsoft.com" , "pavel@ucw.cz" , "john.allen@amd.com" , "bsingharora@gmail.com" , "mike.kravetz@oracle.com" , "dethoma@microsoft.com" , "andrew.cooper3@citrix.com" , "oleg@redhat.com" , "keescook@chromium.org" , "gorcunov@gmail.com" , "arnd@arndb.de" , "Yu, Yu-cheng" , "hpa@zytor.com" , "mingo@redhat.com" , "hjl.tools@gmail.com" , "linux-mm@kvack.org" , "Syromiatnikov, Eugene" , "Yang, Weijiang" , "linux-doc@vger.kernel.org" , "dave.hansen@linux.intel.com" , "Torvalds, Linus" , "Eranian, Stephane" Subject: Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description References: <1cd67ae45fc379fd82d2745190e4caf74e67499e.camel@intel.com> Date: Mon, 03 Jul 2023 20:49:17 +0200 In-Reply-To: (szabolcs's message of "Mon, 3 Jul 2023 19:19:00 +0100") Message-ID: <87r0pox236.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A5FD8140024 X-Stat-Signature: 1yectfhe8p54if33pit6iaiy8d79ij3o X-Rspam-User: X-HE-Tag: 1688410173-721258 X-HE-Meta: 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 lBwLro7F NDsgw20NZPe7RRAYaEncBtD4rRax9qrlTfDEzOJsGQvyBMJDEzZKGfNK3BMpgajHa6FCMF5KDHUdkd5l3RNdH4S3lk3FFGOrtenfUt6nBvR3Ew7YM0l0OAsGPgU6F3o3dR3NqEu1pKE2nxPkL8ErVIJ9ObafTH51y3fwqoC9FBdjJKVEJdqrY9wi+9X5f1bR9yFqnIwDuvOV9ftWdA0Bu9zUAWoL6BgBbx4rs 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: * szabolcs: >> alt shadow stack cannot be transparent to existing software anyway, it > > maybe not in glibc, but a libc can internally use alt shadow stack > in sigaltstack instead of exposing a separate sigaltshadowstack api. > (this is what a strict posix conform implementation has to do to > support shadow stacks), leaking shadow stacks is not a correctness > issue unless it prevents the program working (the shadow stack for > the main thread likely wastes more memory than all the alt stack > leaks. if the leaks become dominant in a thread the sigaltstack > libc api can just fail). It should be possible in theory to carve out pages from sigaltstack and push a shadow stack page and a guard page as part of the signal frame. As far as I understand it, the signal frame layout is not ABI, so it's possible to hide arbitrary stuff in it. I'm just saying that it looks possible, not that it's a good idea. Perhaps that's not realistic with 64K pages, though. Thanks, Florian