linux-kernel - Re: [PATCH v7 01/72] KVM: SVM: nested: Don't allocate VMCB structures on stack

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Date:   Thu, 5 Nov 2020 18:31:53 -0600
From:   Michael Roth <michael.roth@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        Juergen Gross <jgross@...e.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Mike Stunes <mstunes@...are.com>,
        Kees Cook <keescook@...omium.org>, kvm@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Cfir Cohen <cfir@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        virtualization@...ts.linux-foundation.org,
        Martin Radev <martin.b.radev@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, hpa@...or.com,
        Erdem Aktas <erdemaktas@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v7 01/72] KVM: SVM: nested: Don't allocate VMCB
 structures on stack

On Thu, Nov 05, 2020 at 05:38:12PM +0100, Borislav Petkov wrote:
> On Thu, Nov 05, 2020 at 10:24:37AM -0600, Michael Roth wrote:
> > >  out_set_gif:
> > >         svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
> > > -       return 0;
> > > +
> > > +       ret = 0;
> > > +out_free:
> > > +       kfree(save);
> > > +       kfree(ctl);
> > 
> > This change seems to trigger a crash via smm-test.c (and state-test.c) KVM
> > selftest when we call vcpu_load_state->KVM_SET_NESTED_STATE. I think what's
> > happening is we are hitting the 'goto out_set_gif;'
> 
> No out_set_gif upstream anymore after
> 
> d5cd6f340145 ("KVM: nSVM: Avoid freeing uninitialized pointers in svm_set_nested_state()")
> 
> and it looks like you hit the issue this patch is fixing.
> 
> Can you test with the above commit cherrypicked ontop of your what looks
> like 5.9.1-ish tree?
> 
> If that fixes it, we should route this patch to stable.

Hi Boris,

I can confirm that patch fixes the issue. It is indeed a 5.9.1 tree, but
looks like the SEV-ES patches didn't go in until v5.10-rc1 (this tree
had a backport of them), so stable trees shouldn't be affected.

Thanks!

-Mike

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
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