linux-kernel - Re: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page permissions

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Message-ID: <YimT1uYC/3EFR1VV@iki.fi>
Date:   Thu, 10 Mar 2022 07:59:50 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        "Dhanraj, Vijay" <vijay.dhanraj@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...en8.de" <bp@...en8.de>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Zhang, Cathy" <cathy.zhang@...el.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "Shanahan, Mark" <mark.shanahan@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page
 permissions

On Thu, Mar 10, 2022 at 07:43:42AM +0200, Jarkko Sakkinen wrote:
> On Thu, Mar 03, 2022 at 01:44:14PM -0800, Dave Hansen wrote:
> > On 3/3/22 13:23, Reinette Chatre wrote:
> > > Unfortunately MAP_POPULATE is not supported by SGX VMAs because of their
> > > VM_IO and VM_PFNMAP flags. When VMAs with such flags obtain this capability
> > > then I believe that SGX would benefit.
> > 
> > Some Intel folks asked for this quite a while ago.  I think it's
> > entirely doable: add a new vm_ops->populate() function that will allow
> > ignoring VM_IO|VM_PFNMAP if present.
> > 
> > Or, if nobody wants to waste all of the vm_ops space, just add an
> > arch_vma_populate() or something which can call over into SGX.
> > 
> > I'll happily review the patches if anyone can put such a beast together.
> 
> Everyone would be better off, if EAUG's were done unconditionally for
> mmap() after initialization. Nice property is that this needs no core mm
> changes.
> 
> The resource saving argument is at least a bit weak because you might use
> EMODPR for the address range anyway. So you end up doing things just
> slower. And to have good confidentiality, you actually probably want to
> clear also dynamically added pages with EACCEPTCOPY (and zero page) when
> you take them into use.
> 
> I find it also a bit worrying that enclave has direct access to allocate
> kernel resources and trigger ring-0 opcode. I don't like that part at
> all. syscall/ioctl sets the correct barrier, as the host side should be
> and is the resource manager, not the enclave.

Actually, this should be ABI compatible too. I'd expect all kselftests
continue work as they are.

BR, Jarkko