Re: [PATCH v2 0/2] xen/gntdev: Fixes for leaks and VMA splitting

[Demi Marie Obenour]

On Fri, Oct 07, 2022 at 07:17:41AM +0200, Juergen Gross wrote:
> On 03.10.22 00:20, M. Vefa Bicakci wrote:
> > Hi all,
> > 
> > First of all, sorry for the delay!
> > 
> > These patches continue the code review for the following patches:
> >    https://lore.kernel.org/xen-devel/20220912040002.198191-1-m.v.b@xxxxxxxxxx/t/#u
> > 
> > The original description of the patch set is as follows:
> > 
> >    "The changes in this patch series intend to fix the Xen grant device
> >    driver, so that grant mapping leaks caused by partially failed grant
> >    mapping operations are avoided with the first patch, and so that the
> >    splitting of VMAs does not result in incorrectly unmapped grant pages
> >    with the second patch. The second patch also prevents a similar issue
> >    in a double-mapping scenario, where mmap() is used with MAP_FIXED to
> >    map grants over an existing mapping created with the same grants, and
> >    where grant pages are unmapped incorrectly as well."
> > 
> > A summary of the changes from v1 is as follows:
> > - Addressed Juergen's code review comment regarding the first patch.
> > - Amended the description of the second patch to note that the described
> >    issues are encountered with PV domains.
> > 
> > Verification notes:
> > 
> > - I have tested these commits on top of Linux v5.15.70 and v5.15.71, and
> >    I verified that they compile successfully on top of the tag
> >    "next-20220930", which corresponds to the base commit ID included at
> >    the bottom of this e-mail.
> > 
> > - My tests consist of using a kernel with Qubes OS v4.1's patches and
> >    these patches on my main computer for day-to-day tasks, in conjunction
> >    with Qubes OS's version of the Xen hypervisor v4.14.5, with the latter
> >    custom-compiled with CONFIG_DEBUG.
> > 
> > - I used a test program that verifies the following scenarios with an
> >    unprivileged paravirtualized (PV) Xen domain:
> > 
> >    - A program mmap()s two pages from another Xen domain and munmap()s
> >      the pages one by one. This used to result in implicit unmap errors
> >      to be reported by Xen and a general protection fault to be triggered
> >      by Xen in the affected domain, but now works as expected.
> >    - A program mmap()s two pages from another Xen domain and then
> >      attempts to remap (via MAP_FIXED) the same mapping again over the
> >      same virtual address. This used to result in similar issues
> >      (implicit unmap errors and general protection fault), but now is
> >      rejected by the kernel.
> >    - A program mmap()s two pages from another Xen domain and then
> >      attempts to mmap() the same mapping again to a different virtual
> >      address, by passing NULL as mmap()'s first argument. This used to be
> >      rejected by the kernel, and it continues to be rejected by the
> >      kernel.
> > 
> > - Unprivileged PVH Xen domains were also sanity tested with the same
> >    test program. I should note that PVH domains worked as expected
> >    without these patches too.
> > 
> > - Finally, I have verified that the original "g.e. 0x1234 still pending"
> >    issue does not appear after rapidly resizing GUI windows in Qubes OS
> >    v4.1.
> 
> Series pushed to xen/tip.git for-linus-6.1

Thanks!
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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