linux-kernel - Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD memory encryption

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: <b54bd492-9702-5ad7-95da-daf20918d3d9@intel.com>
Date:   Tue, 3 Sep 2019 12:38:25 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>, dri-devel@...ts.freedesktop.org,
        pv-drivers@...are.com, linux-graphics-maintainer@...are.com,
        linux-kernel@...r.kernel.org
Cc:     Thomas Hellstrom <thellstrom@...are.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD
 memory encryption

This whole thing looks like a fascinating collection of hacks. :)

ttm is taking a stack-alllocated "VMA" and handing it to vmf_insert_*()
which obviously are expecting "real" VMAs that are linked into the mm.
It's extracting some pgprot_t information from the real VMA, making a
psuedo-temporary VMA, then passing the temporary one back into the
insertion functions:

> static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> {
...
>         struct vm_area_struct cvma;
...
>                 if (vma->vm_flags & VM_MIXEDMAP)
>                         ret = vmf_insert_mixed(&cvma, address,
>                                         __pfn_to_pfn_t(pfn, PFN_DEV));
>                 else
>                         ret = vmf_insert_pfn(&cvma, address, pfn);

I can totally see why this needs new exports.  But, man, it doesn't seem
like something we want to keep *feeding*.

The real problem here is that the encryption bits from the device VMA's
"true" vma->vm_page_prot don't match the ones that actually get
inserted, probably because the device ptes need the encryption bits
cleared but the system memory PTEs need them set *and* they're mixed
under one VMA.

The thing we need to stop is having mixed encryption rules under one VMA.