linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Michal Hocko <mhocko@suse.com>
To: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Lee Duncan <lduncan@suse.com>, Chris Leech <cleech@redhat.com>,
	Adam Nichols <adam@grimm-co.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-hardening@vger.kernel.org,
	Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer
Date: Wed, 17 Mar 2021 13:08:21 +0100	[thread overview]
Message-ID: <YFHxNT1Pwoslmhxq@dhcp22.suse.cz> (raw)
In-Reply-To: <202103161205.B2181BDE38@keescook>

On Tue 16-03-21 12:08:02, Kees Cook wrote:
> On Tue, Mar 16, 2021 at 09:31:23AM +0100, Michal Hocko wrote:
[...]
> > Also this cannot really be done for configurations with a very limited
> > vmalloc space (32b for example). Those systems are more and more rare
> > but you shouldn't really allow userspace to deplete the vmalloc space.
>
> This sounds like two objections:
> - 32b has a small vmalloc space
> - userspace shouldn't allow depletion of vmalloc space
>
> I'd be happy to make this 64b only. For the latter, I would imagine
> there are other vmalloc-exposed-to-userspace cases, but yes, this would
> be much more direct. Is that a problem in practice?

vmalloc space shouldn't be a problem for 64b systems but I am not sure
how does vmalloc scale with many small allocations. There were some
changes by Uladzislau who might give us more insight (CCed).

> > I would be also curious to see how vmalloc scales with huge number of
> > single page allocations which would be easy to trigger with this patch.
>
> Right -- what the best way to measure this (and what would be "too
> much")?

Proc is used quite heavily for all sorts of monitoring so I would be
worried about a noticeable slow down.

Btw. I still have problems with the approach. seq_file is intended to
provide safe way to dump values to the userspace. Sacrificing
performance just because of some abuser seems like a wrong way to go as
Al pointed out earlier. Can we simply stop the abuse and disallow to
manipulate the buffer directly? I do realize this might be more tricky
for reasons mentioned in other emails but this is definitely worth
doing.

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2021-03-17 12:09 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15 17:48 Kees Cook
2021-03-15 18:33 ` Al Viro
2021-03-15 20:43   ` Kees Cook
2021-03-16  7:24     ` Greg Kroah-Hartman
2021-03-16 12:43       ` Al Viro
2021-03-16 12:55         ` Greg Kroah-Hartman
2021-03-16 13:01         ` Michal Hocko
2021-03-16 19:18         ` Kees Cook
2021-03-17 10:44           ` Greg Kroah-Hartman
2021-03-16  8:31 ` Michal Hocko
2021-03-16 19:08   ` Kees Cook
2021-03-17 12:08     ` Michal Hocko [this message]
2021-03-17 13:34       ` Greg Kroah-Hartman
2021-03-17 14:44         ` Michal Hocko
2021-03-17 14:56           ` Greg Kroah-Hartman
2021-03-17 15:20             ` Michal Hocko
2021-03-17 15:38               ` Greg Kroah-Hartman
2021-03-17 15:48                 ` Michal Hocko
2021-03-17 21:30                 ` Kees Cook
2021-03-18  8:07                   ` Greg Kroah-Hartman
2021-03-18 15:51                     ` Kees Cook
2021-03-18 17:56                       ` Greg Kroah-Hartman
2021-03-19 14:07 ` [seq_file] 5fd6060e50: stress-ng.eventfd.ops_per_sec -49.1% regression kernel test robot
2021-03-19 19:31   ` Kees Cook

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=YFHxNT1Pwoslmhxq@dhcp22.suse.cz \
    --to=mhocko@suse.com \
    --cc=adam@grimm-co.com \
    --cc=adobriyan@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=cleech@redhat.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=keescook@chromium.org \
    --cc=lduncan@suse.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-hardening@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=urezki@gmail.com \
    --subject='Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer' \
    /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

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).