linux-kernel - Re: [PATCH v4 0/2] Fix SEV user-space mapping of unencrypted coherent memory

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Date:   Mon, 16 Mar 2020 13:42:39 +0100
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Christian König <christian.koenig@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v4 0/2] Fix SEV user-space mapping of unencrypted coherent
 memory

Dave, Ingo

On 3/4/20 12:45 PM, Thomas Hellström (VMware) wrote:
> This patchset fixes dma_mmap_coherent() mapping of unencrypted memory in
> otherwise encrypted environments, where it would incorrectly map that memory as
> encrypted.
>
> With SEV and sometimes with SME encryption, The dma api coherent memory is
> typically unencrypted, meaning the linear kernel map has the encryption
> bit cleared. However, default page protection returned from vm_get_page_prot()
> has the encryption bit set. So to compute the correct page protection we need
> to clear the encryption bit.
>
> Also, in order for the encryption bit setting to survive across do_mmap() and
> mprotect_fixup(), We need to make pgprot_modify() aware of it and not touch it.
> Therefore make sme_me_mask part of _PAGE_CHG_MASK and make sure
> pgprot_modify() preserves also cleared bits that are part of _PAGE_CHG_MASK,
> not just set bits. The use of pgprot_modify() is currently quite limited and
> easy to audit.
>
> (Note that the encryption status is not logically encoded in the pfn but in
> the page protection even if an address line in the physical address is used).
>
> The patchset has seen some sanity testing by exporting dma_pgprot() and
> using it in the vmwgfx mmap handler with SEV enabled.
>
> As far as I can tell there are no current users of dma_mmap_coherent() with
> SEV or SME encryption which means that there is no need to CC stable.
>
> Changes since:
> RFC:
> - Make sme_me_mask port of _PAGE_CHG_MASK rather than using it by its own in
>    pgprot_modify().
> v1:
> - Clarify which use-cases this patchset actually fixes.
> v2:
> - Use _PAGE_ENC instead of sme_me_mask in the definition of _PAGE_CHG_MASK
> v3:
> - Added RB from Dave Hansen.
>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Christian König <christian.koenig@....com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
Could we merge this small series through x86?
Patch 2/2 has a

Reviewed-by: Christoph Hellwig<hch@....de>

Please let me know if you want me to resend with that RB added.

Thanks,
Thomas