linux-kernel - Re: [PATCH v38 10/24] mm: Add vm

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Date:   Thu, 24 Sep 2020 12:28:54 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Haitao Huang <haitao.huang@...ux.intel.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        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,
        Dave Hansen <dave.hansen@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "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
Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect()

On Thu, Sep 24, 2020 at 02:11:37PM -0500, Haitao Huang wrote:
> On Wed, 23 Sep 2020 08:50:56 -0500, Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> >I'll categorically deny noexec in the next patch set version.
> >
> >/Jarkko
> 
> There are use cases supported currently in which enclave binary is received
> via IPC/RPC and held in buffers before EADD. Denying noexec altogether would
> break those, right?

No.  noexec only applies to file-backed VMAs, what you're describing is loading
an enclave from an anon VMA, which will still have VM_MAYEXEC.

I believe you're thinking of SELinux's EXECMEM, which is required to execute
from anonymous memory, and which we talked about (more than once) applying to
SGX enclaves.

That being said, I still dislike the idea of requiring VM_MAYEXEC, it's a hack
that doesn't really buy us much, if anything.