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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id i12sm17141581pgd.56.2021.10.25.10.51.22 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Oct 2021 10:51:23 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.13\)) Subject: Re: [PATCH v2 3/5] x86/mm: check exec permissions on fault From: Nadav Amit In-Reply-To: <37d0b84c-f6ca-15cb-8d78-b6b5a9496da7@intel.com> Date: Mon, 25 Oct 2021 10:51:21 -0700 Cc: Linux-MM , LKML , Andrea Arcangeli , Andrew Cooper , Andrew Morton , Andy Lutomirski , Dave Hansen , Peter Xu , Peter Zijlstra , Thomas Gleixner , Will Deacon , Yu Zhao , Nick Piggin , x86@kernel.org Content-Transfer-Encoding: 7bit Message-Id: References: <20211021122112.592634-1-namit@vmware.com> <20211021122112.592634-4-namit@vmware.com> <00C2DC4B-A77D-4B32-B7F7-2291830BC2D2@gmail.com> <37d0b84c-f6ca-15cb-8d78-b6b5a9496da7@intel.com> To: Dave Hansen X-Mailer: Apple Mail (2.3654.120.0.1.13) X-Stat-Signature: isorzc8u3ttxc45b3ojo3tuc14wmrc87 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2AB5E20019D7 Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=XOE89h3u; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf26.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com X-HE-Tag: 1635184286-6087 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 Oct 25, 2021, at 10:45 AM, Dave Hansen wrote: > > On 10/25/21 9:19 AM, Nadav Amit wrote: >> That was my first version, but I was concerned that perhaps there is >> some strange scenario in which both X86_PF_WRITE and X86_PF_INSN can >> be set. That is the reason that Peter asked you whether this is >> something that might happen. >> >> If you confirm they cannot be both set, I would the version you just >> mentioned. > > I'm pretty sure they can't be set together on any sane hardware. A > bonkers hypervisor or CPU could do it of course, but they'd be crazy. > > BTW, feel free to add a WARN_ON_ONCE() if WRITE and INSN are both set. > That would be a nice place to talk about the assumption. > I can do that. But be aware that if the assumption is broken, it might lead to the application getting stuck in an infinite loop of page-faults instead of receiving SIGSEGV.