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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <187bfd4d-89dd-c12b-fa07-d4e0b09ee37d@intel.com>
Date:   Mon, 29 Nov 2021 08:41:25 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     Brijesh Singh <brijesh.singh@....com>,
        Peter Gonda <pgonda@...gle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Tom Lendacky <Thomas.Lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP)
 Hypervisor Support

On 11/25/21 2:05 AM, Joerg Roedel wrote:
> On Wed, Nov 24, 2021 at 09:48:14AM -0800, Dave Hansen wrote:
>> 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.
> The kmap case is guarded by KVM code, which locks the page first so that
> the guest can't change the page state, then checks the page state, and
> if it is shared does the kmap and the access.
> 
> This should turn an RMP fault in the kernel which is not covered in the
> uaccess exception table into a fatal error.

Let's say something does process_vm_readv() where the pid is a qemu
process and it is writing to a guest private memory area.  The syscall
will eventually end up in process_vm_rw_single_vec() which does:

>                 pinned_pages = pin_user_pages_remote(mm, pa, pinned_pages,
>                                                      flags, process_pages,
>                                                      NULL, &locked);
...
>                 rc = process_vm_rw_pages(process_pages,
>                                          start_offset, bytes, iter,
>                                          vm_write);


and eventually in copy_page_from_iter():

>                 void *kaddr = kmap_local_page(page);
>                 size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);
>                 kunmap_local(kaddr);

The kernel access to 'kaddr+offset' shouldn't fault.  How does the KVM
code thwart that kmap_local_page()?