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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id ix6-20020a170902f80600b0017691eb7e17sm13273549plb.239.2022.10.20.15.54.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Oct 2022 15:54:50 -0700 (PDT) Date: Thu, 20 Oct 2022 15:54:49 -0700 From: Kees Cook To: "Edgecombe, Rick P" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "Yu, Yu-cheng" , "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" , "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" , "Moreira, Joao" , "tglx@linutronix.de" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "mingo@redhat.com" , "Shankar, Ravi V" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Subject: Re: [PATCH v2 24/39] x86/cet/shstk: Add user-mode shadow stack support Message-ID: <202210201553.8CE1524C5@keescook> References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-25-rick.p.edgecombe@intel.com> <202210031203.EB0DC0B7DD@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666306492; a=rsa-sha256; cv=none; b=xT1d4Y62llU7I2yvX30sbmlMjT0rtkq3tXX2K7KNjUs9AlX0djUpkF7ZimiX1J/gB7UNIW cXKr0GCKpovOWfdFdBQU/P87qwTa+anC7StNsBY7gCBvHiXCjFzrecRIdGQf0PGt//yM6Q 4u/AmOrc8TFS5D6z25+82kNJB4UyQI8= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=cGhvA8iP; spf=pass (imf21.hostedemail.com: domain of keescook@chromium.org designates 209.85.210.180 as permitted sender) smtp.mailfrom=keescook@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666306492; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=XWJxeWTUeSOc8Yughfud6jj7osnbJGAbeWyZP3k0hEY=; b=ZoHf+WW4rVn0QQ7eWKKpboIeK60F29cWBXR26aI2O8VE4qHPsVFa/1M3nc0ikd5MKNYvo5 caHqslmtCnzI1+hft/ELZf1fKb22QwTAhbC7OWsYEMOv5dpYQnB85zGLe0q0cjSvGSHIdt kQ+/4son3/mI91GxZtLMMm7gnjkPhLM= X-Stat-Signature: 8xt5rmkahne3kthyxcyg74oewd9cpfz5 X-Rspamd-Queue-Id: 347E61C002B Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=cGhvA8iP; spf=pass (imf21.hostedemail.com: domain of keescook@chromium.org designates 209.85.210.180 as permitted sender) smtp.mailfrom=keescook@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1666306491-96036 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 Thu, Oct 20, 2022 at 09:29:38PM +0000, Edgecombe, Rick P wrote: > The code used to use shstk->base and shstk->size to keep track of if > shadow stack was enabled. I'm not sure why to zero it now. Just > defensively or did you see a concrete issue? Just to be defensive. It's not fast path by any means, to better to have values that make a bit of sense there. *shrug* It just stood out as feeling "missing" while I was reading the code. -- Kees Cook