Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 10 Feb 2022 17:48:55 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Brijesh Singh <brijesh.singh@amd.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        brijesh.ksingh@gmail.com, tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when
 changing C-bit
Message-ID: <YgVB94suNJLjzalt@zn.tnic>
References: <20220209181039.1262882-1-brijesh.singh@amd.com>
 <20220209181039.1262882-22-brijesh.singh@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20220209181039.1262882-22-brijesh.singh@amd.com>
Precedence: bulk

On Wed, Feb 09, 2022 at 12:10:15PM -0600, Brijesh Singh wrote:
> The set_memory_{encrypted,decrypted}() are used for changing the pages
> from decrypted (shared) to encrypted (private) and vice versa.
> When SEV-SNP is active, the page state transition needs to go through
> additional steps done by the guest.
> 
> If the page is transitioned from shared to private, then perform the
> following after the encryption attribute is set in the page table:
> 
> 1. Issue the page state change VMGEXIT to add the memory region in
>    the RMP table.
> 2. Validate the memory region after the RMP entry is added.
> 
> To maintain the security guarantees, if the page is transitioned from
> private to shared, then perform the following before encryption attribute
> is removed from the page table:
> 
> 1. Invalidate the page.
> 2. Issue the page state change VMGEXIT to remove the page from RMP table.
> 
> To change the page state in the RMP table, use the Page State Change
> VMGEXIT defined in the GHCB specification.
> 
> The GHCB specification provides the flexibility to use either 4K or 2MB
> page size in during the page state change (PSC) request. For now use the
> 4K page size for all the PSC until RMP page size tracking is supported
> in the kernel.

This commit message sounds familiar because I've read it before - patch
18 - and it looks copied. So I've turned into a simple one which says it
all:

    x86/mm: Validate memory when changing the C-bit

    Add the needed functionality to change pages state from shared
    to private and vice-versa using the Page State Change VMGEXIT as
    documented in the GHCB spec.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette