David Gibson wrote:

On Wed, Nov 29, 2017 at 11:38:22AM -0500, Serhii Popovych wrote:

quoted

It is possible to trigger use after free during HPT resize
causing host kernel to crash. More details and analysis of
the problem can be found in change with corresponding subject
(KVM: PPC: Book3S HV: Fix use after free in case of multiple
resize requests).

We need some changes to prepare for the fix, especially
make ->error in HPT resize instance single point for
tracking allocation state, improve kvmppc_allocate_hpt()
and kvmppc_free_hpt() so they can be used more safely.

See individual commit description message to get more
information on changes presented.

I spoke with Paul Mackerras about these patches on IRC today.  We want
this as a fix, ASAP, in 4.15.  However, he's uncomfortable with
pushing some of extra cleanups which aren't necessary for the bug fix
this late for 4.15, and was having trouble following what was the core
of the fix.  He was also nervous about the addition of more BUG_ON()s.

Good, no problem, cleanups will be pushed additionally.

To avoid the round trip to Ukraine time and back, I've made revised
versions of patches 1 & 3 which should apply standalone, replaced the
BUG_ON()s with WARN_ON()s and revised the commit messages to better
explain the crucial part of the fix.

However, I've run out of time to test them.

I did the same test as for this v1 series and found no problem with v2
you sent to me: it seems patch improving kvmppc_allocate_hpt() and
kvmppc_free_hpt() isn't actually necessary as I was thinking when
submitting v1.

Serhii,  I'll send you my revised patches shortly.  Can you please
test them and repost.  Then you can rebase patches 2 & 4 from this
series on top of the revised patches and post those separately (as a
cleanup with less urgency than the actual fix).

Tested with same test case as with v1: no problem so far.

A couple of people have also suggested CCing kvm@vger.kernel.org on
the next round in addition to the lists already included.

Done.

-- 
Thanks,
Serhii