linux-kernel - Re: [PATCH] x86/sev: Check whether SEV or SME is supported first

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Message-ID: <YLZy+JR7TNEeNA6C@zn.tnic>
Date:   Tue, 1 Jun 2021 19:48:40 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>, Pu Wen <puwen@...on.cn>,
        Joerg Roedel <jroedel@...e.de>, x86@...nel.org,
        joro@...tes.org, dave.hansen@...ux.intel.com, peterz@...radead.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        sashal@...nel.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/sev: Check whether SEV or SME is supported first

On Tue, Jun 01, 2021 at 05:16:12PM +0000, Sean Christopherson wrote:
> The bug isn't limited to out-of-spec hardware.  At the point of #GP, sme_enable()
> has only verified the max leaf is greater than 0x8000001f, it has not verified
> that 0x8000001f is actually supported.  The APM itself declares several leafs
> between 0x80000000 and 0x8000001f as reserved/unsupported, so we can't argue that
> 0x8000001f must be supported if the max leaf is greater than 0x8000001f.

If a hypervisor says that 0x8000001f is supported but then we explode
when reading MSR_AMD64_SEV, then hypervisor gets to keep both pieces.

We're not going to workaround all possible insane hardware/hypervisor
configurations just because they dropped the ball.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette