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[209.85.221.47]) by smtp.gmail.com with ESMTPSA id v18-20020a170906293200b0073022b796a7sm1403183ejd.93.2022.08.09.11.27.38 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Aug 2022 11:27:38 -0700 (PDT) Received: by mail-wr1-f47.google.com with SMTP id p10so15212423wru.8 for ; Tue, 09 Aug 2022 11:27:38 -0700 (PDT) X-Received: by 2002:a05:6000:1888:b0:222:ca41:dc26 with SMTP id a8-20020a056000188800b00222ca41dc26mr6957079wri.442.1660069658303; Tue, 09 Aug 2022 11:27:38 -0700 (PDT) MIME-Version: 1.0 References: <20220808073232.8808-1-david@redhat.com> In-Reply-To: <20220808073232.8808-1-david@redhat.com> From: Linus Torvalds Date: Tue, 9 Aug 2022 11:27:22 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Andrew Morton , Greg Kroah-Hartman , Axel Rasmussen , Peter Xu , Hugh Dickins , Andrea Arcangeli , Matthew Wilcox , Vlastimil Babka , John Hubbard , Jason Gunthorpe Content-Type: text/plain; charset="UTF-8" ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660069661; 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=IqVJxNw31cQs7x7vLdkBRYf56RsQMoz2IVQHanq9IpQ=; b=ZbkPiCqWViVjBdGSVfijL0a7UaHoR0OdEDRk1OYdj9auE3XoRduttgjJIziBYzya/HJSnd AFsBvjP+hQ6cg9Aui45QDW+7t+mp4atE+0XlwgB6BAQsRoKW4/7B/nF6/NwzctUGN+8wmi OYiOO4Gwva/uN5kVJiLAvGNR5oiukKg= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=Mz533wEe; dmarc=none; spf=pass (imf02.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.218.42 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660069661; a=rsa-sha256; cv=none; b=nRR952EQE0BssGIM1tlX5wQ+ZjC4b2JfY0oJni4RKlt1vCLPijWlx31is6Et0C3CK99bS1 5hbKGg5T9gSRyGatteVzw0kXqg5cNkOt0YNStjTsVwY92NiBwJ39r26PeXfMWSrqMF7s8A VXM/skaaudK7r1od/5oOgNO/D7V+4Pg= Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=Mz533wEe; dmarc=none; spf=pass (imf02.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.218.42 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org X-Rspamd-Server: rspam02 X-Stat-Signature: 4cmzgsxhzpyuho7ybrrh8dojn8cnw3xt X-Rspamd-Queue-Id: 414A280178 X-Rspam-User: X-HE-Tag: 1660069661-377449 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: I'm still reading through this, but STOP DOING THIS On Mon, Aug 8, 2022 at 12:32 AM David Hildenbrand wrote: > > + VM_BUG_ON(!is_cow_mapping(vma->vm_flags)); Using BUG_ON() for debugging is simply not ok. And saying "but it's just a VM_BUG_ON()" does not change *anything*. At least Fedora enables that unconditionally for normal people, it is not some kind of "only VM people do this". Really. BUG_ON() IS NOT FOR DEBUGGING. Stop it. Now. If you have a condition that must not happen, you either write that condition into the code, or - if you are convinced it cannot happen - you make it a WARN_ON_ONCE() so that people can report it to you. The BUG_ON() will just make the machine die. And for the facebooks and googles of the world, the WARN_ON() will be sufficient. Linus