linux-kernel - Re: [RFCv2 15/16] KVM: Unmap protected pages from direct mapping

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Date:   Wed, 21 Oct 2020 18:49:47 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "kirill@...temov.name" <kirill@...temov.name>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "liran.alon@...cle.com" <liran.alon@...cle.com>,
        "wad@...omium.org" <wad@...omium.org>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "Kleen, Andi" <andi.kleen@...el.com>
Subject: Re: [RFCv2 15/16] KVM: Unmap protected pages from direct mapping

On Tue, 2020-10-20 at 09:18 +0300, Kirill A. Shutemov wrote:
> If the protected memory feature enabled, unmap guest memory from
> kernel's direct mappings.
> 
> Migration and KSM is disabled for protected memory as it would
> require a
> special treatment.
> 
So do we care about this scenario where a malicious userspace causes a
kernel oops? I'm not sure if it's prevented somehow.

CPU0 (exercising other kernel functionality)	CPU1
						mark page shared
page = get_user_pages(!FOLL_KVM)
						mark page private
kmap(page)
access unmapped page and oops