linux-kernel - Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect

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Message-ID: <X+ESkna2z3WjjniN@google.com>
Date:   Mon, 21 Dec 2020 14:24:34 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Nadav Amit <nadav.amit@...il.com>, Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        stable <stable@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect

On Mon, Dec 21, 2020 at 12:26:22PM -0800, Linus Torvalds wrote:
> On Mon, Dec 21, 2020 at 12:23 PM Nadav Amit <nadav.amit@...il.com> wrote:
> >
> > Using mmap_write_lock() was my initial fix and there was a strong pushback
> > on this approach due to its potential impact on performance.
> 
> From whom?
> 
> Somebody who doesn't understand that correctness is more important
> than performance? And that userfaultfd is not the most important part
> of the system?
> 
> The fact is, userfaultfd is CLEARLY BUGGY.
> 
>           Linus

Fair enough.

Nadav, for your patch (you might want to update the commit message).

Reviewed-by: Yu Zhao <yuzhao@...gle.com>

While we are all here, there is also clear_soft_dirty() that could
use a similar fix...