linux-kernel - Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207

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Date:   Wed, 13 Nov 2019 07:38:14 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
Subject: Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207

On 12.11.19 22:21, Paolo Bonzini wrote:
> CVE-2018-12207 is a microarchitectural implementation issue
> that could allow an unprivileged local attacker to cause system wide
> denial-of-service condition.
> 
> Privileged software may change the page size (ex. 4KB, 2MB, 1GB) in the
> paging structures, without following such paging structure changes with
> invalidation of the TLB entries corresponding to the changed pages. In
> this case, the attacker could invoke instruction fetch, which will result
> in the processor hitting multiple TLB entries, reporting a machine check
> error exception, and ultimately hanging the system.
> 
> The attached patches mitigate the vulnerability by making huge pages
> non-executable. The processor will not be able to execute an instruction
> residing in a large page (ie. 2MB, 1GB, etc.) without causing a trap into
> the host kernel/hypervisor; KVM will then break the large page into 4KB
> pages and gives executable permission to 4KB pages.

When reading MCE, error code 0150h, ie. SRAR, I was wondering if that 
couldn't simply be handled by the host. But I suppose the symptom of 
that erratum is not "just" regular recoverable MCE, rather 
sometimes/always an unrecoverable CPU state, despite the error code, right?

Jan

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