Linux-Fsdevel Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Stefano Garzarella <sgarzare@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
	Kees Cook <keescook@chromium.org>,
	Pavel Begunkov <asml.silence@gmail.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Matthew Wilcox <willy@infradead.org>,
	Jann Horn <jannh@google.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	strace-devel@lists.strace.io, io-uring@vger.kernel.org,
	Linux API <linux-api@vger.kernel.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: strace of io_uring events?
Date: Tue, 21 Jul 2020 17:58:48 +0200	[thread overview]
Message-ID: <20200721155848.32xtze5ntvcmjv63@steredhat> (raw)
In-Reply-To: <CALCETrXSPdiVCgh3h=q7w9RyiKnp-=8jOHoFHX=an0cWqK7bzQ@mail.gmail.com>

On Tue, Jul 21, 2020 at 08:27:34AM -0700, Andy Lutomirski wrote:
> On Fri, Jul 17, 2020 at 1:02 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
> >
> > On Thu, Jul 16, 2020 at 08:12:35AM -0700, Kees Cook wrote:
> > > On Thu, Jul 16, 2020 at 03:14:04PM +0200, Stefano Garzarella wrote:
> 
> > > access (IIUC) is possible without actually calling any of the io_uring
> > > syscalls. Is that correct? A process would receive an fd (via SCM_RIGHTS,
> > > pidfd_getfd, or soon seccomp addfd), and then call mmap() on it to gain
> > > access to the SQ and CQ, and off it goes? (The only glitch I see is
> > > waking up the worker thread?)
> >
> > It is true only if the io_uring istance is created with SQPOLL flag (not the
> > default behaviour and it requires CAP_SYS_ADMIN). In this case the
> > kthread is created and you can also set an higher idle time for it, so
> > also the waking up syscall can be avoided.
> 
> I stared at the io_uring code for a while, and I'm wondering if we're
> approaching this the wrong way. It seems to me that most of the
> complications here come from the fact that io_uring SQEs don't clearly
> belong to any particular security principle.  (We have struct creds,
> but we don't really have a task or mm.)  But I'm also not convinced
> that io_uring actually supports cross-mm submission except by accident
> -- as it stands, unless a user is very careful to only submit SQEs
> that don't use user pointers, the results will be unpredictable.
> Perhaps we can get away with this:
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 74bc4a04befa..92266f869174 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7660,6 +7660,20 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int,
> fd, u32, to_submit,
>      if (!percpu_ref_tryget(&ctx->refs))
>          goto out_fput;
> 
> +    if (unlikely(current->mm != ctx->sqo_mm)) {
> +        /*
> +         * The mm used to process SQEs will be current->mm or
> +         * ctx->sqo_mm depending on which submission path is used.
> +         * It's also unclear who is responsible for an SQE submitted
> +         * out-of-process from a security and auditing perspective.
> +         *
> +         * Until a real usecase emerges and there are clear semantics
> +         * for out-of-process submission, disallow it.
> +         */
> +        ret = -EACCES;
> +        goto out;
> +    }
> +
>      /*
>       * For SQ polling, the thread will do all submissions and completions.
>       * Just return the requested submit count, and wake the thread if
> 
> If we can do that, then we could bind seccomp-like io_uring filters to
> an mm, and we get obvious semantics that ought to cover most of the
> bases.
> 
> Jens, Christoph?
> 
> Stefano, what's your intended usecase for your restriction patchset?
> 

Hi Andy,
my use case concerns virtualization. The idea, that I described in the
proposal of io-uring restrictions [1], is to share io_uring CQ and SQ queues
with a guest VM for block operations.

In the PoC that I realized, there is a block device driver in the guest that
uses io_uring queues coming from the host to submit block requests.

Since the guest is not trusted, we need restrictions to allow only
a subset of syscalls on a subset of file descriptors and memory.


Cheers,
Stefano

[1] https://lore.kernel.org/io-uring/20200609142406.upuwpfmgqjeji4lc@steredhat/


  parent reply	other threads:[~2020-07-21 15:59 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 11:12 Miklos Szeredi
2020-07-15 14:35 ` Andy Lutomirski
2020-07-15 17:11   ` Matthew Wilcox
2020-07-15 19:42     ` Pavel Begunkov
2020-07-15 20:09       ` Miklos Szeredi
2020-07-15 20:20         ` Pavel Begunkov
2020-07-15 23:07           ` Kees Cook
2020-07-16 13:14             ` Stefano Garzarella
2020-07-16 15:12               ` Kees Cook
2020-07-17  8:01                 ` Stefano Garzarella
2020-07-21 15:27                   ` Andy Lutomirski
2020-07-21 15:31                     ` Jens Axboe
2020-07-21 17:23                       ` Andy Lutomirski
2020-07-21 17:30                         ` Jens Axboe
2020-07-21 17:44                           ` Andy Lutomirski
2020-07-21 18:39                             ` Jens Axboe
2020-07-21 19:44                               ` Andy Lutomirski
2020-07-21 19:48                                 ` Jens Axboe
2020-07-21 19:56                                 ` Andres Freund
2020-07-21 19:37                         ` Andres Freund
2020-07-21 15:58                     ` Stefano Garzarella [this message]
2020-07-23 10:39                       ` Stefan Hajnoczi
2020-07-23 13:37                       ` Colin Walters
2020-07-24  7:25                         ` Stefano Garzarella
2020-07-16 13:17             ` Aleksa Sarai
2020-07-16 15:19               ` Kees Cook
2020-07-17  8:17               ` Cyril Hrubis
2020-07-16 16:24             ` Andy Lutomirski
2020-07-16  0:12     ` tytso

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=20200721155848.32xtze5ntvcmjv63@steredhat \
    --to=sgarzare@redhat.com \
    --cc=asml.silence@gmail.com \
    --cc=axboe@kernel.dk \
    --cc=christian.brauner@ubuntu.com \
    --cc=hch@lst.de \
    --cc=io-uring@vger.kernel.org \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=miklos@szeredi.hu \
    --cc=mtk.manpages@gmail.com \
    --cc=stefanha@redhat.com \
    --cc=strace-devel@lists.strace.io \
    --cc=willy@infradead.org \
    --subject='Re: strace of io_uring events?' \
    /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).