From: Dan Williams <email@example.com>
To: Greg KH <firstname.lastname@example.org>
Cc: Arnd Bergmann <email@example.com>, Ingo Molnar <firstname.lastname@example.org>,
Kees Cook <email@example.com>,
Russell King <firstname.lastname@example.org>,
Andrew Morton <email@example.com>,
Linux Kernel Mailing List <firstname.lastname@example.org>,
Linux MM <email@example.com>
Subject: Re: [PATCH v2] /dev/mem: Revoke mappings when a driver claims the region
Date: Tue, 19 May 2020 11:27:02 -0700 [thread overview]
Message-ID: <CAPcyv4gTkWx_q4sDXVyS+ybh0Nj7ybPUXGC4HCHQCO4eGxXwiQ@mail.gmail.com> (raw)
On Tue, May 19, 2020 at 5:11 AM Greg KH <firstname.lastname@example.org> wrote:
> On Tue, May 19, 2020 at 12:03:06AM -0700, Dan Williams wrote:
> > Close the hole of holding a mapping over kernel driver takeover event of
> > a given address range.
> > Commit 90a545e98126 ("restrict /dev/mem to idle io memory ranges")
> > introduced CONFIG_IO_STRICT_DEVMEM with the goal of protecting the
> > kernel against scenarios where a /dev/mem user tramples memory that a
> > kernel driver owns. However, this protection only prevents *new* read(),
> > write() and mmap() requests. Established mappings prior to the driver
> > calling request_mem_region() are left alone.
> > Especially with persistent memory, and the core kernel metadata that is
> > stored there, there are plentiful scenarios for a /dev/mem user to
> > violate the expectations of the driver and cause amplified damage.
> > Teach request_mem_region() to find and shoot down active /dev/mem
> > mappings that it believes it has successfully claimed for the exclusive
> > use of the driver. Effectively a driver call to request_mem_region()
> > becomes a hole-punch on the /dev/mem device.
> > The typical usage of unmap_mapping_range() is part of
> > truncate_pagecache() to punch a hole in a file, but in this case the
> > implementation is only doing the "first half" of a hole punch. Namely it
> > is just evacuating current established mappings of the "hole", and it
> > relies on the fact that /dev/mem establishes mappings in terms of
> > absolute physical address offsets. Once existing mmap users are
> > invalidated they can attempt to re-establish the mapping, or attempt to
> > continue issuing read(2) / write(2) to the invalidated extent, but they
> > will then be subject to the CONFIG_IO_STRICT_DEVMEM checking that can
> > block those subsequent accesses.
> > Cc: Arnd Bergmann <email@example.com>
> > Cc: Ingo Molnar <firstname.lastname@example.org>
> > Cc: Kees Cook <email@example.com>
> > Cc: Russell King <firstname.lastname@example.org>
> > Cc: Andrew Morton <email@example.com>
> > Cc: Greg Kroah-Hartman <firstname.lastname@example.org>
> > Fixes: 90a545e98126 ("restrict /dev/mem to idle io memory ranges")
> > Signed-off-by: Dan Williams <email@example.com>
> > ---
> > Changes since v1 :
> > - updated the changelog to describe the usage of unmap_mapping_range().
> > No other logic changes:
> > : http://firstname.lastname@example.org
> > Greg, Andrew,
> > I have a regression test for this case now. This was found by an
> > intermittent data corruption scenario on pmem from a test tool using
> > /dev/mem.
> Ick, why are test tools messing around in /dev/mem :)
Yeah, I'm all for useful tools, just not at the expense of kernel integrity.
> Anyway, this seems sane to me, want me to take it through my tree?
Yes please, seems to belong with the driver core.
next prev parent reply other threads:[~2020-05-19 18:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 7:03 [PATCH v2] /dev/mem: Revoke mappings when a driver claims the region Dan Williams
2020-05-19 12:11 ` Greg KH
2020-05-19 18:27 ` Dan Williams [this message]
2020-05-20 5:44 ` Greg KH
2020-05-19 18:46 ` Matthew Wilcox
2020-05-19 19:36 ` Dan Williams
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:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* 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).