linux-kernel - Re: [PATCH, RFC 47/62] mm: Restrict MKTME memory encryption to anonymous VMAs

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Date:   Fri, 14 Jun 2019 17:07:05 -0700
From:   Alison Schofield <alison.schofield@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>, linux-mm@...ck.org,
        kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 47/62] mm: Restrict MKTME memory encryption to
 anonymous VMAs

On Fri, Jun 14, 2019 at 01:55:20PM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 05:44:07PM +0300, Kirill A. Shutemov wrote:
> > From: Alison Schofield <alison.schofield@...el.com>
> > 
> > Memory encryption is only supported for mappings that are ANONYMOUS.
> > Test the VMA's in an encrypt_mprotect() request to make sure they all
> > meet that requirement before encrypting any.
> > 
> > The encrypt_mprotect syscall will return -EINVAL and will not encrypt
> > any VMA's if this check fails.
> > 
> > Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> This should be folded back into the initial implemention, methinks.

It is part of the initial implementation. I looked for
places to split the implementation into smaller,
reviewable patches, hence this split. None of it gets
built until the CONFIG_X86_INTEL_MKTME is introduced
in a later patch.

The encrypt_mprotect() patchset is ordered like this:
1) generalize mprotect to support the mktme extension
2) wire up encrypt_mprotect()
3) implement encrypt_mprotect()
4) keep reference counts on encryption keys (was VMAs)
5) (this patch) restrict to anonymous VMAs.
  
I thought Patch 5) was a small, but meaningful split. It 
accentuates the fact that MKTME is restricted to anonymous
memory.

Alas, I want to make it logical to review, so I'll move it.