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[209.85.221.48]) by smtp.gmail.com with ESMTPSA id d20-20020a170906c21400b007307c557e31sm1473095ejz.106.2022.08.09.13.15.06 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Aug 2022 13:15:06 -0700 (PDT) Received: by mail-wr1-f48.google.com with SMTP id v3so15587625wrp.0 for ; Tue, 09 Aug 2022 13:15:06 -0700 (PDT) X-Received: by 2002:a5d:638b:0:b0:220:6e1a:8794 with SMTP id p11-20020a5d638b000000b002206e1a8794mr15513397wru.193.1660076105927; Tue, 09 Aug 2022 13:15:05 -0700 (PDT) MIME-Version: 1.0 References: <20220808073232.8808-1-david@redhat.com> <91e18a2f-c93d-00b8-7c1b-6d8493c3b2d5@redhat.com> In-Reply-To: <91e18a2f-c93d-00b8-7c1b-6d8493c3b2d5@redhat.com> From: Linus Torvalds Date: Tue, 9 Aug 2022 13:14:49 -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-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660076108; a=rsa-sha256; cv=none; b=T5I4svAJbQf0WIeuVcjorXdzVx+IQANsF+0tr2FCa7zk4wULhFmdUgiLIYQ3jFhT6L5d6C GZ9x2opN1tC+T2BDIgsYavAMsx2VwjHnH7nrrih8SfENV21nZDYdWGiQr4L+WGc9pgdUJv Bj9DBBQYWxS3VKZoPok+aIpV08Sc1Ow= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660076108; 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=X1/mYkVHU3QQELeXoM1reH5RSgIloRBIOFMBth8wCSU=; b=l7Kq19YIfiC0KG4szxaQmAzLoDezReh2V/RXaIeT+DqIM6WC+b+OV7Q+lVJVU1H1LZHi7A tOqpmW0yWVkXGfCy4hWbkIPzTcUPgQiuaptyPYZNnP0a00+ugsN7b2j6pcWdxEsaZwjHMp zuqcBu3UTitUc7FePTsBw7NXC6snMBY= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b="FGG/j0qA"; spf=pass (imf02.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.218.42 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-Stat-Signature: bsqcgdub6fhrqcikse7a4xfadupkugbr X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8881880178 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b="FGG/j0qA"; spf=pass (imf02.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.218.42 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-HE-Tag: 1660076108-665651 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 Tue, Aug 9, 2022 at 1:07 PM David Hildenbrand wrote: > > > /* But FOLL_FORCE has no effect on shared mappings */ > > if (vma->vm_flags & MAP_SHARED) > > return false; > > I'd actually rather check for MAP_MAYSHARE here, which is even stronger. > Thoughts? Hmm. Adding the test for both is basically free (all those vm_flags checks end up being a bit mask and compare), so no objections. For some reason I though VM_SHARED and VM_MAYSHARE end up always being the same bits, and it was a mistake to make them two bits in the first place (unlike the read/write/exec bits that can are about mprotect), But as there are two bits, I'm sure somebody ends up touching one and not the other. So yeah, I don't see any downside to just checking both bits. [ That said, is_cow_mapping() only checks VM_SHARED, so if they are ever different, that's a potential source of confusion ] Linus