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[91.12.101.77]) by smtp.gmail.com with ESMTPSA id h18sm2040722wrs.75.2021.09.27.10.06.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Sep 2021 10:06:43 -0700 (PDT) Subject: Re: [RFC PATCH] userfaultfd: support control over mm of remote PIDs To: Nadav Amit Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrea Arcangeli , Mike Rapoport , Peter Xu References: <20210926170637.245699-1-namit@vmware.com> <83827672-0996-4c25-9991-697ad443b6b3@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: <21c6a41d-3f65-6a49-f604-b75ef53d2910@redhat.com> Date: Mon, 27 Sep 2021 19:06:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dJhisrrn; spf=none (imf27.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1010B70000A0 X-Stat-Signature: yedihag8e59ctupkt1rtmmx5m9wn1ezn X-HE-Tag: 1632762406-118240 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 27.09.21 12:19, Nadav Amit wrote: > > >> On Sep 27, 2021, at 2:29 AM, David Hildenbrand wrote: >> >> On 26.09.21 19:06, Nadav Amit wrote: >>> From: Nadav Amit >>> Non-cooperative mode is useful but only for forked processes. >>> Userfaultfd can be useful to monitor, debug and manage memory of remote >>> processes. >>> To support this mode, add a new flag, UFFD_REMOTE_PID, and an optional >>> second argument to the userfaultfd syscall. When the flag is set, the >>> second argument is assumed to be the PID of the process that is to be >>> monitored. Otherwise the flag is ignored. >>> The syscall enforces that the caller has CAP_SYS_PTRACE to prevent >>> misuse of this feature. >> >> What supposed to happen if the target process intents to use uffd itself? > > Thanks for the quick response. > > First, sorry that I mistakenly dropped the changes to userfaultfd.h > that define UFFD_REMOTE_PID. Didn't even notice it :) > > As for your question: there are standard ways to deal with such cases, > similarly to when a debugged program wants to use PTRACE. One way is > to block the userfaultfd syscall, using seccomp. Another way is to do > chaining using ptrace (although using ptrace for anything is > challenging). > > It is also possible to add tailor something specific to userfaultfd, > but I think seccomp is a good enough solution. I am open to suggestions. If we have something already in place to handle PTRACE, we'd better reuse what's already there. Thanks! -- Thanks, David / dhildenb