From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:37112) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SzPVo-0007RJ-Ln for qemu-devel@nongnu.org; Thu, 09 Aug 2012 05:58:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SzPVn-00038s-Fa for qemu-devel@nongnu.org; Thu, 09 Aug 2012 05:58:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9946) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SzPVn-00038o-72 for qemu-devel@nongnu.org; Thu, 09 Aug 2012 05:58:39 -0400 Message-ID: <502389B5.4020506@redhat.com> Date: Thu, 09 Aug 2012 12:58:13 +0300 From: Avi Kivity MIME-Version: 1.0 References: <20120724023657.6600.52706.stgit@ltc189.sdl.hitachi.co.jp> <20120724023718.6600.68836.stgit@ltc189.sdl.hitachi.co.jp> <20120809090312.GH3280@amit.redhat.com> <502381EA.80805@hitachi.com> <20120809095514.GJ3280@amit.redhat.com> In-Reply-To: <20120809095514.GJ3280@amit.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH 2/6] virtio/console: Add a failback for unstealable pipe buffer List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Amit Shah Cc: Rusty Russell , Arnd Bergmann , qemu-devel@nongnu.org, Frederic Weisbecker , Yoshihiro YUNOMAE , yrl.pp-manager.tt@hitachi.com, linux-kernel@vger.kernel.org, Borislav Petkov , virtualization@lists.linux-foundation.org, Herbert Xu , "Franch Ch. Eigler" , Ingo Molnar , Mathieu Desnoyers , Steven Rostedt , Anthony Liguori , Greg Kroah-Hartman , Masami Hiramatsu On 08/09/2012 12:55 PM, Amit Shah wrote: > On (Thu) 09 Aug 2012 [18:24:58], Masami Hiramatsu wrote: >> (2012/08/09 18:03), Amit Shah wrote: >> > On (Tue) 24 Jul 2012 [11:37:18], Yoshihiro YUNOMAE wrote: >> >> From: Masami Hiramatsu >> >> >> >> Add a failback memcpy path for unstealable pipe buffer. >> >> If buf->ops->steal() fails, virtio-serial tries to >> >> copy the page contents to an allocated page, instead >> >> of just failing splice(). >> >> >> >> Signed-off-by: Masami Hiramatsu >> >> Cc: Amit Shah >> >> Cc: Arnd Bergmann >> >> Cc: Greg Kroah-Hartman >> >> --- >> >> >> >> drivers/char/virtio_console.c | 28 +++++++++++++++++++++++++--- >> >> 1 files changed, 25 insertions(+), 3 deletions(-) >> >> >> >> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c >> >> index fe31b2f..911cb3e 100644 >> >> --- a/drivers/char/virtio_console.c >> >> +++ b/drivers/char/virtio_console.c >> >> @@ -794,7 +794,7 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf, >> >> struct splice_desc *sd) >> >> { >> >> struct sg_list *sgl = sd->u.data; >> >> - unsigned int len = 0; >> >> + unsigned int offset, len; >> >> >> >> if (sgl->n == MAX_SPLICE_PAGES) >> >> return 0; >> >> @@ -807,9 +807,31 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf, >> >> >> >> len = min(buf->len, sd->len); >> >> sg_set_page(&(sgl->sg[sgl->n]), buf->page, len, buf->offset); >> >> - sgl->n++; >> >> - sgl->len += len; >> >> + } else { >> >> + /* Failback to copying a page */ >> >> + struct page *page = alloc_page(GFP_KERNEL); >> > >> > I prefer zeroing out the page. If there's not enough data to be >> > filled in the page, the remaining data can be leaked to the host. >> >> Yeah, it is really easy to fix that. >> But out of curiosity, would that be really a problem? >> I guess that host can access any guest page if need. If that >> is right, is that really insecure to leak randomly allocated >> unused page to the host? > > I'm not sure if there is a way to really attack, but just something I > had thought about: the host kernel can access any guest page, that's > not something we can prevent. > > However, if qemu is restricted from accessing guest pages, and the > guest shares this page with qemu for r/w purposes via the virtio > channel, a qemu exploit can expose guest data to host userspace. > > I agree this is completely theoretical; can someone else with more > insight confirm or deny my apprehensions? qemu can read and write any guest page (for the guest it controls). -- error compiling committee.c: too many arguments to function