Messages in this thread | | | Date | Thu, 09 Aug 2012 12:58:13 +0300 | From | Avi Kivity <> | Subject | Re: [RFC PATCH 2/6] virtio/console: Add a failback for unstealable pipe buffer |
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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 <masami.hiramatsu.pt@hitachi.com> >> >> >> >> 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 <masami.hiramatsu.pt@hitachi.com> >> >> Cc: Amit Shah <amit.shah@redhat.com> >> >> Cc: Arnd Bergmann <arnd@arndb.de> >> >> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >> >> --- >> >> >> >> 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
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