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From: Andi Kleen <ak@linux.intel.com>
To: David Rientjes <rientjes@google.com>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Jon Grimm <jon.grimm@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Christoph Hellwig <hch@lst.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	x86@kernel.org, linux-mm@kvack.org
Subject: Re: AMD SEV-SNP/Intel TDX: validation of memory pages
Date: Tue, 2 Feb 2021 14:37:55 -0800	[thread overview]
Message-ID: <20210202223755.GM27611@tassilo.jf.intel.com> (raw)
In-Reply-To: <7515a81a-19e-b063-2081-3f5e79f0f7a8@google.com>

On Mon, Feb 01, 2021 at 05:51:09PM -0800, David Rientjes wrote:
> the new PVALIDATE instruction[1].  This sets the Validated flag in the
> Reverse Map Table (RMP) for a guest addressable page, which opts into
> hardware and firmware integrity protection.  This may only be done by the
> guest itself and until that time, the guest cannot access the page.

Another important point is that we need to reject (panic) any accepts for 
memory that have already been accepted, to avoid an attacker
replacing memory. This means that any memory requires some
metadata.

>  - Any need for validating memory that is not backed by struct page that
>    needs to be special-cased

We may not have struct page for firmware structures for example.

> 
>  - Any concerns about this for the DMA layer

It would be needed to handle directly assigned devices because they
could do DMA to not yet accepted memory.

> 
> One possibility for minimal disruption to the boot entry code is to
> require the guest BIOS to validate 4GB and below, and then leave 4GB and
> above to be done lazily (the true amount of memory will actually be less
> due to the MMIO hole).

This would seem fragile to me, requiring Linux to never access any
memory >4GB early. Better would be if Linux accepts everything it
needs early by itself.

-Andi


  parent reply	other threads:[~2021-02-02 22:38 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-02  1:51 AMD SEV-SNP/Intel TDX: validation of memory pages David Rientjes
2021-02-02 13:17 ` Matthew Wilcox
2021-02-02 16:02 ` Kirill A. Shutemov
2021-02-03  0:16   ` Brijesh Singh
2021-02-11 17:46     ` Sean Christopherson
2021-02-02 22:37 ` Andi Kleen [this message]
2021-02-11 20:46 ` Peter Zijlstra
2021-02-12 13:19 ` Joerg Roedel
2021-02-12 14:17   ` Peter Zijlstra
2021-02-12 14:53     ` Joerg Roedel
2021-02-12 15:19       ` Peter Zijlstra
2021-02-12 15:28         ` Joerg Roedel
2021-02-12 16:12           ` Peter Zijlstra
2021-02-12 16:18             ` Joerg Roedel
2021-02-12 16:45               ` Peter Zijlstra
2021-02-12 17:48                 ` Dave Hansen
2021-02-12 18:22                   ` Sean Christopherson
2021-02-12 18:38                     ` Andy Lutomirski
2021-02-12 18:43                       ` Sean Christopherson
2021-02-12 18:46                     ` Dave Hansen
2021-02-12 19:24                       ` Sean Christopherson
2021-02-16 10:00                 ` Joerg Roedel
2021-02-16 14:27                   ` Andi Kleen
2021-02-16 14:46                     ` Peter Zijlstra
2021-02-16 15:59                       ` Paolo Bonzini
2021-02-16 16:25                         ` Joerg Roedel
2021-02-16 16:48                           ` Paolo Bonzini
2021-02-16 18:26                             ` Joerg Roedel
2021-02-16 18:33                               ` Paolo Bonzini
2021-02-16 16:47                         ` Peter Zijlstra
2021-02-16 16:57                         ` Andy Lutomirski
2021-02-16 17:05                           ` Paolo Bonzini
2021-02-16 16:55                       ` Andi Kleen
2021-02-12 21:42             ` Andi Kleen
2021-02-12 21:58               ` Peter Zijlstra
2021-02-12 22:39                 ` Andi Kleen
2021-02-12 22:46                   ` Andy Lutomirski
2021-02-13  9:38                   ` Peter Zijlstra
2021-02-12 23:51                 ` Paolo Bonzini
2021-03-23  9:33 ` Joerg Roedel

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