Re: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support

Vlastimil Babka
2021-11-24T19:35:39Z

On 11/24/21 18:48, Dave Hansen wrote:
> On 11/24/21 8:03 AM, Joerg Roedel wrote:
>> On Mon, Nov 22, 2021 at 02:51:35PM -0800, Dave Hansen wrote:
>>> My preference would be that we never have SEV-SNP code in the kernel
>>> that can panic() the host from guest userspace. If that means waiting
>>> until there's common guest unmapping infrastructure around, then I think
>>> we should wait.
>> Can you elaborate how to crash host kernel from guest user-space? If I
>> understood correctly it was about crashing host kernel from _host_
>> user-space.
>
> Sorry, I misspoke there.
>
> My concern is about crashing the host kernel. It appears that *host*
> userspace can do that quite easily by inducing the host kernel to access
> some guest private memory via a kernel mapping.

I thought some of the scenarios discussed here also went along "guest
(doesn't matter if userspace or kernel) shares a page with host, invokes
some host kernel operation and in parallel makes the page private again".

>> I think the RMP-fault path in the page-fault handler needs to take the
>> uaccess exception tables into account before actually causing a panic.
>> This should solve most of the problems discussed here.
>
> That covers things like copy_from_user(). It does not account for
> things where kernel mappings are used, like where a
> get_user_pages()/kmap() is in play.
>