From: Dan Williams <dan.j.williams@intel.com>
To: Kees Cook <keescook@chromium.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Russell King <linux@arm.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH v4] /dev/mem: Revoke mappings when a driver claims the region
Date: Thu, 7 Apr 2022 16:43:10 -0700 [thread overview]
Message-ID: <CAPcyv4hFxVAKgUqt-mua5_1NZkfyKKFL-3F0tSWuSmD=4Z1sBw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4htK6Ur4-B=cfkQeOD__9s7ZfxMTo+uCCPVDLG=_WNy7A@mail.gmail.com>
On Thu, Apr 7, 2022 at 11:47 AM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Wed, Apr 6, 2022 at 12:46 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > *thread necromancy*
>
> It's alive!
>
> >
> > Hi Dan,
> >
> > I'm doing a KSPP bug scrub and am reviewing
> > https://github.com/KSPP/linux/issues/74 again.
> >
> > Do you have a chance to look at this? I'd love a way to make mmap()
> > behave the same way as read() for the first meg of /dev/mem.
>
> You want 0-reads or SIGBUS when attempting to access the first 1MB?
>
> Because it sounds like what you want is instead of loudly failing with
> -EPERM in drivers/char/mem.c::mmap_mem() you want it to silently
> succeed but swap in the zero page, right? Otherwise if it's SIGBUS
> then IO_STRICT_DEVMEM=y + marking that span as IORESOURCE_BUSY will
> "Do the Right Thing (TM).".
In other words, if IO_STRICT_DEVMEM is enabled then the enforcement is
already there at least for anything marked IORESOURCE_BUSY. So if
tools are ok with that protection today, maybe there is no need to do
the zero page dance. I.e. legacy tools the read(2) /dev/mem below 1MB
get zeroes, and apparently no tools were mmap'ing below 1MB otherwise
they would have complained by now? At least Fedora is shipping
IO_STRICT_DEVMEM these days:
https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel-x86_64-fedora.config#_2799
next prev parent reply other threads:[~2022-04-07 23:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-21 21:06 [PATCH v4] /dev/mem: Revoke mappings when a driver claims the region Dan Williams
2020-05-22 3:01 ` Kees Cook
2022-04-06 19:45 ` Kees Cook
2022-04-07 18:47 ` Dan Williams
2022-04-07 23:43 ` Dan Williams [this message]
2022-04-08 3:35 ` Kees Cook
2022-04-08 6:51 ` Dan Williams
2022-04-07 23:46 ` Kees Cook
2021-05-27 20:58 ` Bjorn Helgaas
2021-05-27 21:30 ` Dan Williams
2021-05-28 8:58 ` David Hildenbrand
2021-05-28 16:42 ` Dan Williams
2021-05-28 16:51 ` David Hildenbrand
2021-06-03 3:39 ` Bjorn Helgaas
2021-06-03 4:15 ` Dan Williams
2021-06-03 18:11 ` Bjorn Helgaas
2021-06-03 18:28 ` Dan Williams
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAPcyv4hFxVAKgUqt-mua5_1NZkfyKKFL-3F0tSWuSmD=4Z1sBw@mail.gmail.com' \
--to=dan.j.williams@intel.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=gregkh@linuxfoundation.org \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux@arm.linux.org.uk \
--cc=mingo@redhat.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).