linux-kernel - Re: [PATCH] KVM: Add separate helper for putting borrowed reference to kvm

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Message-ID: <aba06fb62083a7424a10170c074911de8cd4e347.camel@linux.ibm.com>
Date:   Thu, 28 Nov 2019 13:04:30 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paul Mackerras <paulus@...abs.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Add separate helper for putting borrowed reference
 to kvm

On Thu, 2019-11-28 at 14:49 +0100, Paolo Bonzini wrote:
> On 27/11/19 22:57, Leonardo Bras wrote:
> > But on the above case, kvm_put_kvm{,_no_destroy}() would be called
> > with refcount == 1, and if reorder patch is applied, it would not cause
> > any use-after-free error, even on kvm_put_kvm() case.
> 
> I think this is what you're missing: kvm_put_kvm_no_destroy() does not
> protect against bugs in the code that uses it.  It protect against bugs
> _elsewhere_.
> 
> Therefore, kvm_put_kvm_no_destroy() is always a better choice when
> applicable, because it turns bugs in _other parts of the code_ from
> use-after-free to WARN+leak.
> 
> Paolo
> 

Hello Paolo,

Thanks for explaining that! I think I got to understand it better now.

Best regards,
Leonardo

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