From: Jens Axboe <axboe@kernel.dk>
To: Jann Horn <jannh@google.com>
Cc: linux-aio@kvack.org, linux-block@vger.kernel.org,
linux-man <linux-man@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
hch@lst.de, jmoyer@redhat.com, Avi Kivity <avi@scylladb.com>
Subject: Re: [PATCH 05/18] Add io_uring IO interface
Date: Mon, 28 Jan 2019 19:21:27 -0700 [thread overview]
Message-ID: <6ade41f5-1b21-51ec-91f3-d55b77a7c6c1@kernel.dk> (raw)
In-Reply-To: <CAG48ez1qxZLfJzK95kjh0RiQ6kvZLbQhr6Dr0EjBNQB6Fr7NXQ@mail.gmail.com>
On 1/28/19 6:07 PM, Jann Horn wrote:
> On Mon, Jan 28, 2019 at 10:35 PM Jens Axboe <axboe@kernel.dk> wrote:
>> The submission queue (SQ) and completion queue (CQ) rings are shared
>> between the application and the kernel. This eliminates the need to
>> copy data back and forth to submit and complete IO.
> [...]
>> +static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
>> +{
>> + struct io_sq_ring *ring = ctx->sq_ring;
>> + unsigned head;
>> +
>> + /*
>> + * The cached sq head (or cq tail) serves two purposes:
>> + *
>> + * 1) allows us to batch the cost of updating the user visible
>> + * head updates.
>> + * 2) allows the kernel side to track the head on its own, even
>> + * though the application is the one updating it.
>> + */
>> + head = ctx->cached_sq_head;
>> + smp_rmb();
>> + if (head == READ_ONCE(ring->r.tail))
>> + return false;
>> +
>> + head = ring->array[head & ctx->sq_mask];
>> + if (head < ctx->sq_entries) {
>> + s->index = head;
>> + s->sqe = &ctx->sq_sqes[head];
>
> ring->array can be mapped writable into userspace, right? If so: This
> looks like a double-read issue; the compiler might assume that
> ring->array is not modified concurrently and perform separate memory
> accesses for the "if (head < ctx->sq_entries)" check and the
> "&ctx->sq_sqes[head]" computation. Please use READ_ONCE()/WRITE_ONCE()
> for all accesses to memory that userspace could concurrently modify in
> a malicious way.
>
> There have been some pretty severe security bugs caused by missing
> READ_ONCE() annotations around accesses to shared memory; see, for
> example, https://www.blackhat.com/docs/us-16/materials/us-16-Wilhelm-Xenpwn-Breaking-Paravirtualized-Devices.pdf
> . Slides 35-48 show how the code "switch (op->cmd)", where "op" is a
> pointer to shared memory, allowed an attacker to break out of a Xen
> virtual machine because the compiler generated multiple memory
> accesses.
Thanks, I'll update these to use READ/WRITE_ONCE.
>> + ctx->cached_sq_head++;
>> + return true;
>> + }
>> +
>> + /* drop invalid entries */
>> + ctx->cached_sq_head++;
>> + ring->dropped++;
>> + smp_wmb();
>> + return false;
>> +}
> [...]
>> +SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
>> + u32, min_complete, u32, flags, const sigset_t __user *, sig,
>> + size_t, sigsz)
>> +{
>> + struct io_ring_ctx *ctx;
>> + long ret = -EBADF;
>> + struct fd f;
>> +
>> + f = fdget(fd);
>> + if (!f.file)
>> + return -EBADF;
>> +
>> + ret = -EOPNOTSUPP;
>> + if (f.file->f_op != &io_uring_fops)
>> + goto out_fput;
>
> Oh, by the way: If you feel like it, maybe you could add a helper
> fdget_typed(int fd, struct file_operations *f_op), or something like
> that, so that there is less boilerplate code for first doing fdget(),
> then checking ->f_op, and then coding an extra bailout path for that?
> But that doesn't really have much to do with your patchset, feel free
> to ignore this comment.
That's not a bad idea, I think this is a fairly common code pattern.
I'll look into it.
--
Jens Axboe
--
To unsubscribe, send a message with 'unsubscribe linux-aio' in
the body to majordomo@kvack.org. For more info on Linux AIO,
see: http://www.kvack.org/aio/
Don't email: <a href=mailto:"aart@kvack.org">aart@kvack.org</a>
next prev parent reply other threads:[~2019-01-29 2:21 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-28 21:35 [PATCHSET v8] io_uring IO interface Jens Axboe
2019-01-28 21:35 ` [PATCH 01/18] fs: add an iopoll method to struct file_operations Jens Axboe
2019-01-28 21:35 ` [PATCH 02/18] block: wire up block device iopoll method Jens Axboe
2019-01-28 21:35 ` [PATCH 03/18] block: add bio_set_polled() helper Jens Axboe
2019-01-28 21:35 ` [PATCH 04/18] iomap: wire up the iopoll method Jens Axboe
2019-01-28 21:35 ` [PATCH 05/18] Add io_uring IO interface Jens Axboe
2019-01-28 21:53 ` Jeff Moyer
2019-01-28 21:56 ` Jens Axboe
2019-01-28 22:32 ` Jann Horn
2019-01-28 23:46 ` Jens Axboe
2019-01-28 23:59 ` Jann Horn
2019-01-29 0:03 ` Jens Axboe
2019-01-29 0:31 ` Jens Axboe
2019-01-29 0:34 ` Jann Horn
2019-01-29 0:55 ` Jens Axboe
2019-01-29 0:58 ` Jann Horn
2019-01-29 1:01 ` Jens Axboe
2019-02-01 16:57 ` Matt Mullins
2019-02-01 17:04 ` Jann Horn
2019-02-01 17:23 ` Jann Horn
2019-02-01 18:05 ` Al Viro
2019-01-29 1:07 ` Jann Horn
2019-01-29 2:21 ` Jann Horn
2019-01-29 2:54 ` Jens Axboe
2019-01-29 3:46 ` Jens Axboe
2019-01-29 15:56 ` Jann Horn
2019-01-29 16:06 ` Jens Axboe
2019-01-29 2:21 ` Jens Axboe [this message]
2019-01-29 1:29 ` Jann Horn
2019-01-29 1:31 ` Jens Axboe
2019-01-29 1:32 ` Jann Horn
2019-01-29 2:23 ` Jens Axboe
2019-01-29 7:12 ` Bert Wesarg
2019-01-29 12:12 ` Florian Weimer
2019-01-29 13:35 ` Jens Axboe
2019-01-28 21:35 ` [PATCH 06/18] io_uring: add fsync support Jens Axboe
2019-01-28 21:35 ` [PATCH 07/18] io_uring: support for IO polling Jens Axboe
2019-01-29 17:24 ` Christoph Hellwig
2019-01-29 18:31 ` Jens Axboe
2019-01-29 19:10 ` Jens Axboe
2019-01-29 20:35 ` Jeff Moyer
2019-01-29 20:37 ` Jens Axboe
2019-01-28 21:35 ` [PATCH 08/18] fs: add fget_many() and fput_many() Jens Axboe
2019-01-28 21:35 ` [PATCH 09/18] io_uring: use fget/fput_many() for file references Jens Axboe
2019-01-28 21:56 ` Jann Horn
2019-01-28 22:03 ` Jens Axboe
2019-01-28 21:35 ` [PATCH 10/18] io_uring: batch io_kiocb allocation Jens Axboe
2019-01-29 17:26 ` Christoph Hellwig
2019-01-29 18:14 ` Jens Axboe
2019-01-28 21:35 ` [PATCH 11/18] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-01-28 21:35 ` [PATCH 12/18] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-01-28 23:35 ` Jann Horn
2019-01-28 23:50 ` Jens Axboe
2019-01-29 0:36 ` Jann Horn
2019-01-29 1:25 ` Jens Axboe
2019-01-28 21:35 ` [PATCH 13/18] io_uring: add file set registration Jens Axboe
2019-01-28 21:35 ` [PATCH 14/18] io_uring: add submission polling Jens Axboe
2019-01-28 21:35 ` [PATCH 15/18] io_uring: add io_kiocb ref count Jens Axboe
2019-01-29 17:26 ` Christoph Hellwig
2019-01-28 21:35 ` [PATCH 16/18] io_uring: add support for IORING_OP_POLL Jens Axboe
2019-01-28 21:35 ` [PATCH 17/18] io_uring: allow workqueue item to handle multiple buffered requests Jens Axboe
2019-01-28 21:35 ` [PATCH 18/18] io_uring: add io_uring_event cache hit information Jens Axboe
[not found] <20190123153536.7081-1-axboe@kernel.dk>
[not found] ` <20190123153536.7081-6-axboe@kernel.dk>
2019-01-28 14:57 ` [PATCH 05/18] Add io_uring IO interface Christoph Hellwig
2019-01-28 16:26 ` Jens Axboe
2019-01-28 16:34 ` Christoph Hellwig
2019-01-28 19:32 ` Jens Axboe
2019-01-28 18:25 ` Jens Axboe
2019-01-29 6:30 ` Christoph Hellwig
2019-01-29 11:58 ` Arnd Bergmann
2019-01-29 15:20 ` Jens Axboe
2019-01-29 16:18 ` Arnd Bergmann
2019-01-29 16:19 ` Jens Axboe
2019-01-29 16:26 ` Arnd Bergmann
2019-01-29 16:28 ` Jens Axboe
2019-01-29 16:46 ` Arnd Bergmann
2019-01-29 0:47 ` Andy Lutomirski
2019-01-29 1:20 ` Jens Axboe
2019-01-29 6:45 ` Christoph Hellwig
2019-01-29 12:05 ` Arnd Bergmann
2019-01-31 5:11 ` Andy Lutomirski
2019-01-31 16:37 ` Jens Axboe
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=6ade41f5-1b21-51ec-91f3-d55b77a7c6c1@kernel.dk \
--to=axboe@kernel.dk \
--cc=avi@scylladb.com \
--cc=hch@lst.de \
--cc=jannh@google.com \
--cc=jmoyer@redhat.com \
--cc=linux-aio@kvack.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-man@vger.kernel.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).