Re: [PATCH v1] libvhost-user: fix VHOST_USER_REM_MEM_REG skipping mmap_addr

[Stefan Hajnoczi]

On Thu, Oct 14, 2021 at 04:52:48AM +0000, Raphael Norwitz wrote:
> On Wed, Oct 13, 2021 at 10:40:46AM +0100, Stefan Hajnoczi wrote:
> > On Mon, Oct 11, 2021 at 10:10:47PM +0200, David Hildenbrand wrote:
> > > We end up not copying the mmap_addr of all existing regions, resulting
> > > in a SEGFAULT once we actually try to map/access anything within our
> > > memory regions.
> > > 
> > > Fixes: 875b9fd97b34 ("Support individual region unmap in libvhost-user")
> > > Cc: qemu-stable@nongnu.org
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > > Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
> > > Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > Cc: Coiby Xu <coiby.xu@gmail.com>
> > > Signed-off-by: David Hildenbrand <david@redhat.com>
> > > ---
> > >  subprojects/libvhost-user/libvhost-user.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/subprojects/libvhost-user/libvhost-user.c 
> > > b/subprojects/libvhost-user/libvhost-user.c
> > > index bf09693255..787f4d2d4f 100644
> > > --- a/subprojects/libvhost-user/libvhost-user.c
> > > +++ b/subprojects/libvhost-user/libvhost-user.c
> > > @@ -816,6 +816,7 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
> > >              shadow_regions[j].gpa = dev->regions[i].gpa;
> > >              shadow_regions[j].size = dev->regions[i].size;
> > >              shadow_regions[j].qva = dev->regions[i].qva;
> > > +            shadow_regions[j].mmap_addr = dev->regions[i].mmap_addr;
> > >              shadow_regions[j].mmap_offset = dev->regions[i].mmap_offset;
> > >              j++;
> > >          } else {
> > 
> > Raphael: Some questions about vu_rem_mem_reg():
> > 
> > - What ensures that shadow_regions[VHOST_USER_MAX_RAM_SLOTS] is large
> >   enough? The add_mem_reg/set_mem_table code doesn't seem to check
> >   whether there is enough space in dev->regions[] before adding regions.
> >
> 
> Correct - it does not check if there is enough space as is. I can add that.
> 
> > - What happens when the master populated dev->regions[] with multiple
> >   copies of the same region? dev->nregions is only decremented once and
> >   no longer accurately reflects the number of elements in
> >   dev->regions[].
> 
> That case is also not accounted for. I will add it.
> 
> > 
> > libvhost-user must not trust the vhost-user master since vhost-user
> > needs to provide process isolation. Please add input validation.
> > 
> 
> Got it - let me start working on a series.

Great, thank you!

Stefan

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