linux-kernel - Re: [PATCH 05/25] x86/sgx: Introduce runtime protection bits

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Date:   Sat, 8 Jan 2022 17:45:41 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Haitao Huang <haitao.huang@...ux.intel.com>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Andy Lutomirski <luto@...nel.org>, dave.hansen@...ux.intel.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com,
        linux-sgx@...r.kernel.org, x86@...nel.org, seanjc@...gle.com,
        kai.huang@...el.com, cathy.zhang@...el.com, cedric.xing@...el.com,
        haitao.huang@...el.com, mark.shanahan@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/25] x86/sgx: Introduce runtime protection bits

On Fri, Jan 07, 2022 at 10:14:29AM -0600, Haitao Huang wrote:
> > > > OK, so the question is: do we need both or would a mechanism just
> > > to extend
> > > > permissions be sufficient?
> > > 
> > > I do believe that we need both in order to support pages having only
> > > the permissions required to support their intended use during the
> > > time the
> > > particular access is required. While technically it is possible to grant
> > > pages all permissions they may need during their lifetime it is safer to
> > > remove permissions when no longer required.
> > 
> > So if we imagine a run-time: how EMODPR would be useful, and how using it
> > would make things safer?
> > 
> In scenarios of JIT compilers, once code is generated into RW pages,
> modifying both PTE and EPCM permissions to RX would be a good defensive
> measure. In that case, EMODPR is useful.

What is the exact threat we are talking about?

/Jarkko