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From:   Souptick Joarder <jrdr.linux@gmail.com>
Date:   Mon, 9 Nov 2020 09:08:12 +0530
Message-ID: <CAFqt6zbC_-y8FAyGLv_QG2VMSa8HhfR+sd=W-E4eyuWfgSXnDQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user_pages*()
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>
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On Sun, Nov 8, 2020 at 10:30 AM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 11/7/20 8:12 PM, Tetsuo Handa wrote:
> > On 2020/11/08 11:17, John Hubbard wrote:
> >>> Excuse me, but Documentation/core-api/pin_user_pages.rst says
> >>> "CASE 5: Pinning in order to _write_ to the data within the page"
> >>> while tomoyo_dump_page() is for "_read_ the data within the page".
> >>> Do we want to convert to pin_user_pages_remote() or lock_page() ?
> >>>
> >>
> >> Sorry, I missed the direction here, was too focused on the Case 5
> >> aspect. Yes. Case 5 (which, again, I think we're about to re-document)
> >> is only about *writing* to data within the page.
> >>
> >> So in this case, where it is just reading from the page, I think it's
> >> already from a gup vs pup point of view.
> >>
> >> btw, it's not clear to me whether the current code is susceptible to any
> >> sort of problem involving something writing to the page while it
> >> is being dumped (I am curious). But changing from gup to pup wouldn't
> >> fix that, if it were a problem. It a separate question from this patch.
> >
> > The "struct page" tomoyo_dump_page() accesses is argv/envp arguments passed
> > to execve() syscall. Therefore, these pages are not visible from threads
> > except current thread, and thus there is no possibility that these pages
> > are modified by other threads while current thread is reading.
> >
>
> Perfect. So since I accidentally left out the word "correct" above (I meant
> to write, "it's already correct"), let me be extra clear: Souptick, we
> should just drop this patch.
>

Agreed. I will drop this patch.