linux-kernel - Re: [PATCH 0/4] Fix use after free in HPT resizing code and related minor improvements

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Message-ID: <87indmsmw8.fsf@concordia.ellerman.id.au>
Date:   Mon, 04 Dec 2017 23:22:47 +1100
From:   Michael Ellerman <michael@...erman.id.au>
To:     David Gibson <david@...son.dropbear.id.au>,
        Serhii Popovych <spopovyc@...hat.com>
Cc:     linux-kernel@...r.kernel.org, paulus@...ba.org,
        linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 0/4] Fix use after free in HPT resizing code and related minor improvements

David Gibson <david@...son.dropbear.id.au> writes:

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

As was I.

> 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

Thanks.

cheers