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Tue, 07 Mar 2023 09:00:52 -0500 X-MC-Unique: IhkD_1szN0qSCW-h4ox-0w-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 88A7929DD9A8; Tue, 7 Mar 2023 14:00:12 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.80]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5562D492C18; Tue, 7 Mar 2023 14:00:04 +0000 (UTC) From: Florian Weimer To: szabolcs.nagy@arm.com Cc: "Edgecombe, Rick P" , "david@redhat.com" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Yu, Yu-cheng" , "Eranian, Stephane" , "kirill.shutemov@linux.intel.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "broonie@kernel.org" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "jamorris@linux.microsoft.com" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "debug@rivosinc.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "mike.kravetz@oracle.com" , "pavel@ucw.cz" , "andrew.cooper3@citrix.com" , "john.allen@amd.com" , "rppt@kernel.org" , "nd@arm.com" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" , "akpm@linux-foundation.org" Subject: Re: [PATCH v7 01/41] Documentation/x86: Add CET shadow stack description References: <636de4a28a42a082f182e940fbd8e63ea23895cc.camel@intel.com> <9714f724b53b04fdf69302c6850885f5dfbf3af5.camel@intel.com> <87wn3tsuxf.fsf@oldenburg.str.redhat.com> Date: Tue, 07 Mar 2023 15:00:02 +0100 In-Reply-To: (szabolcs's message of "Tue, 7 Mar 2023 13:03:41 +0000") Message-ID: <87ilfcoe59.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 10.11.54.9 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4A499140046 X-Stat-Signature: kfu843m1xxzjsbkbsg8iuchhi53e4ntp X-HE-Tag: 1678197663-761289 X-HE-Meta: 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 oOWFgyXh qJQC9q3rXdV/87xBKn9CIzu7q+KoQGYai83O8sndeWuZzffs/ln2+KfryyMbxlV0B0QLbyUu5v6/Y4BKJURF4mYEBkJI28FEjk0Nv50mYUUTjcWhuPgwtLGNaJZeC4jSRtGySkcB4M8bOmxtkwz6v6vRKF/jc61NqiYibwc99fXRKfTtzoqe1FcAVbZLnetR+RfKnqGnwtrj7h/7RTXcLMgjKdBw5SFICYl3TH8/TEK7DEvqpizD9xqcJ/g== 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: > changing/disabling the alt stack is not valid while a handler is > executing on it. if we don't allow jumping out and back to an > alt stack (swapcontext) then there can be only one alt stack > live per thread and change/disable can do the shadow stack free. > > if jump back is allowed (linux even makes it race-free with > SS_AUTODISARM) then the life-time of alt stack is extended > beyond change/disable (jump back to an unregistered alt stack). > > to support jump back to an alt stack the requirements are > > 1) user has to manage an alt shadow stack together with the alt > stack (requies user code change, not just libc). > > 2) kernel has to push a restore token on the thread shadow stack > on signal entry (at least in case of alt shadow stack, and > deal with corner cases around shadow stack overflow). We need to have a story for stackful coroutine switching as well, not just for sigaltstack. I hope that we can use OpenJDK (Project Loom) and QEMU as guinea pigs. If we have something that works for both, hopefully that covers a broad range of scenarios. Userspace coordination can eventually be handled by glibc; we can deallocate alternate stacks on thread exit fairly easily (at least compared to the current stack 8-). Thanks, Florian