Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user_pages*()

[John Hubbard]

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.

thanks,
--
John Hubbard
NVIDIA