linux-kernel - Re: [PATCH v40 10/24] mm: Add 'mprotect' hook to struct vm_operations

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Date:   Wed, 18 Nov 2020 19:39:50 -0600
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Andy Lutomirski" <luto@...nel.org>, "Dr. Greg" <greg@...ellic.com>
Cc:     "Dave Hansen" <dave.hansen@...el.com>,
        "Jarkko Sakkinen" <jarkko.sakkinen@...ux.intel.com>,
        "X86 ML" <x86@...nel.org>, linux-sgx@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        "Sean Christopherson" <sean.j.christopherson@...el.com>,
        Linux-MM <linux-mm@...ck.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Matthew Wilcox" <willy@...radead.org>,
        "Jethro Beekman" <jethro@...tanix.com>,
        "Darren Kenny" <darren.kenny@...cle.com>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, "Borislav Petkov" <bp@...en8.de>,
        "Xing, Cedric" <cedric.xing@...el.com>, chenalexchen@...gle.com,
        "Conrad Parker" <conradparker@...gle.com>, cyhanish@...gle.com,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Svahn, Kai" <kai.svahn@...el.com>,
        "Keith Moyer" <kmoy@...gle.com>,
        "Christian Ludloff" <ludloff@...gle.com>,
        "Neil Horman" <nhorman@...hat.com>,
        "Nathaniel McCallum" <npmccallum@...hat.com>,
        "Patrick Uiterwijk" <puiterwijk@...hat.com>,
        "David Rientjes" <rientjes@...gle.com>,
        "Thomas Gleixner" <tglx@...utronix.de>, yaozhangx@...gle.com,
        "Mikko Ylinen" <mikko.ylinen@...el.com>
Subject: Re: [PATCH v40 10/24] mm: Add 'mprotect' hook to struct
 vm_operations_struct

On Mon, 16 Nov 2020 12:00:23 -0600, Dr. Greg <greg@...ellic.com> wrote:

> On Thu, Nov 12, 2020 at 02:41:00PM -0800, Andy Lutomirski wrote:
>
> Good morning, I hope the week is starting well for everyone.
>
>> On Thu, Nov 12, 2020 at 1:31 PM Dave Hansen <dave.hansen@...el.com>  
>> wrote:
>> >
>> > On 11/12/20 12:58 PM, Dr. Greg wrote:
>> > > @@ -270,11 +270,10 @@ static int sgx_vma_mprotect(struct  
>> vm_area_struct *vma,
>> > >                           struct vm_area_struct **pprev, unsigned  
>> long start,
>> > >                           unsigned long end, unsigned long newflags)
>> > >  {
>> > > -     int ret;
>> > > +     struct sgx_encl *encl = vma->vm_private_data;
>> > >
>> > > -     ret = sgx_encl_may_map(vma->vm_private_data, start, end,  
>> newflags);
>> > > -     if (ret)
>> > > -             return ret;
>> > > +     if ( test_bit(SGX_ENCL_INITIALIZED, &encl->flags) )
>> > > +             return -EACCES;
>> > >
>> > >       return mprotect_fixup(vma, pprev, start, end, newflags);
>> > >  }
>> >
>> > This rules out mprotect() on running enclaves.  Does that break any
>> > expectations from enclave authors, or take away capabilities that  
>> folks
>> > need?
>
>> It certainly prevents any scheme in which an enclave coordinates
>> with the outside world to do W-and-then-X JIT inside.  I'm also not
>> convinced it has any real effect at all unless there's some magic I
>> missed to prevent someone from using mmap(2) to effectively change
>> permissions.
>
> The patch that I posted yesterday addresses the security issue for
> both mmap and mprotect by trapping the permission change request at
> the level of the sgx_encl_may_map() function.
>
> With respect to the W-and-then-X JIT issue, the stated purpose of the
> driver is to implement basic SGX functionality, which is SGX1
> semantics, it has been stated formally for a year by the developers
> themselves that they are not entertaining a driver that addresses any
> of the issues associated with non-static memory permissions.
>

The JIT issue is applicable even to SGX1 platforms. We can do EADD with  
EPCM.RWX in sec_info and with PTE.RW, EINIT, then mprotect to set PTE.RX  
when JIT is done.

Haitao