linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHk-=wiY_g+SSjncZi8sO=LrxXmMox0NO7K34-Fs653XVXheGg@mail.gmail.com>
Date:   Thu, 17 Sep 2020 12:51:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Peter Xu <peterx@...hat.com>, John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On Thu, Sep 17, 2020 at 12:38 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> Looking for awhile, this now looks reasonable and
> doable. page_maybe_dma_pinned() was created for exactly this kind of
> case.
>
> I've attached a dumb sketch for the pte level (surely wrong! I have
> never looked at this part of the mm before!) at the end of this
> message.

This looks conceptually fine to me.

But as mentioned, I think I'd be even happier if we added a "thsi vma
has seen a page pin event" flag to the vma flags, and didn't rely
_just_ on the page_maybe_dma_pinned() check, which migth be triggered
by those fork-happy loads.

Side note: I wonder if that COW mapping check could be entirely within
that vm_normal_page() path.

Because how could a non-normal page be a COW page and not already
write-protected?

But that's a separate issue, it's just how your patch makes that odd
case more obvious.

            Linus