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Mon, 21 Dec 2020 16:24:43 -0800 (PST) Received: from google.com ([2620:15c:183:200:7220:84ff:fe09:2d90]) by smtp.gmail.com with ESMTPSA id w9sm14146363ilq.43.2020.12.21.16.24.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Dec 2020 16:24:42 -0800 (PST) Date: Mon, 21 Dec 2020 17:24:38 -0700 From: Yu Zhao To: Linus Torvalds Cc: Peter Xu , Nadav Amit , Andrea Arcangeli , linux-mm , lkml , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , stable , Minchan Kim , Andy Lutomirski , Will Deacon , Peter Zijlstra Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect Message-ID: References: <9E301C7C-882A-4E0F-8D6D-1170E792065A@gmail.com> <1FCC8F93-FF29-44D3-A73A-DF943D056680@gmail.com> <20201221223041.GL6640@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Mon, Dec 21, 2020 at 04:11:01PM -0800, Linus Torvalds wrote: > On Mon, Dec 21, 2020 at 4:00 PM Yu Zhao wrote: > > > > My first instinct is to be conservative and revert 09854ba94c6a ("mm: > > do_wp_page() simplification") so people are less likely to come back > > and complain about performance issues from holding mmap lock for > > write when clearing pte_write. > > Well, the thing is, that simplificaiton was actually part of fixing a > real regression wrt GUP. > > Reverting that would break a308c71bf1e6 ("mm/gup: Remove enfornced COW > mechanism"). > > And that one was the (better) fix for commit 17839856fd58 that fixed a > real security issue, but did it with a big hammer that then caused > problems for uffd-wp (and some other loads). There's a bit more > context in the merge message in commit b25d1dc9474e Merge branch > 'simplify-do_wp_page'. > > So while that commit 09854ba94c6a on its own is "just" a > simplification, it's actually part of a bigger series that fixes > serious problems. > > Linus Well, that settles it then. I don't any better idea that is as safe as what Nadav has.