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[134.134.136.126]) by mx.google.com with ESMTPS id 33si3196230ply.10.2019.06.07.13.14.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 07 Jun 2019 13:14:14 -0700 (PDT) Received-SPF: pass (google.com: domain of yu-cheng.yu@intel.com designates 134.134.136.126 as permitted sender) client-ip=134.134.136.126; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yu-cheng.yu@intel.com designates 134.134.136.126 as permitted sender) smtp.mailfrom=yu-cheng.yu@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Jun 2019 13:14:13 -0700 X-ExtLoop1: 1 Received: from yyu32-desk1.sc.intel.com ([143.183.136.147]) by orsmga002.jf.intel.com with ESMTP; 07 Jun 2019 13:14:12 -0700 Message-ID: <0e505563f7dae3849b57fb327f578f41b760b6f7.camel@intel.com> Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function From: Yu-cheng Yu To: Dave Hansen , Andy Lutomirski Cc: Peter Zijlstra , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Date: Fri, 07 Jun 2019 13:06:10 -0700 In-Reply-To: <4b448cde-ee4e-1c95-0f7f-4fe694be7db6@intel.com> References: <20190606200926.4029-1-yu-cheng.yu@intel.com> <20190606200926.4029-4-yu-cheng.yu@intel.com> <20190607080832.GT3419@hirez.programming.kicks-ass.net> <20190607174336.GM3436@hirez.programming.kicks-ass.net> <34E0D316-552A-401C-ABAA-5584B5BC98C5@amacapital.net> <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> <4b448cde-ee4e-1c95-0f7f-4fe694be7db6@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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 Fri, 2019-06-07 at 13:00 -0700, Dave Hansen wrote: > On 6/7/19 12:49 PM, Yu-cheng Yu wrote: > > > > > > This also gives us an excellent opportunity to make it read-only as seen > > > from > > > userspace to prevent exploits from just poking it full of ones before > > > redirecting execution. > > > > GLIBC sets bits only for legacy code, and then makes the bitmap read- > > only. That > > avoids most issues: > > > > To populate bitmap pages, mprotect() is required. > > Reading zero bitmap pages would not waste more physical memory, right? > > Huh, how does glibc know about all possible past and future legacy code > in the application? When dlopen() gets a legacy binary and the policy allows that, it will manage the bitmap: If a bitmap has not been created, create one. Set bits for the legacy code being loaded. Yu-cheng