linux-kernel - Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user

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: <CAFqt6zbC_-y8FAyGLv_QG2VMSa8HhfR+sd=W-E4eyuWfgSXnDQ@mail.gmail.com>
Date:   Mon, 9 Nov 2020 09:08:12 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user_pages*()

On Sun, Nov 8, 2020 at 10:30 AM John Hubbard <jhubbard@...dia.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.