linux-kernel - Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct vm_operations

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Message-ID: <20201117181614.GG8524@kernel.org>
Date:   Tue, 17 Nov 2020 20:16:14 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <dave.hansen@...el.com>,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com, bp@...en8.de,
        cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        haitao.huang@...el.com, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, npmccallum@...hat.com, puiterwijk@...hat.com,
        rientjes@...gle.com, tglx@...utronix.de, yaozhangx@...gle.com,
        mikko.ylinen@...el.com
Subject: Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct
 vm_operations_struct

On Fri, Nov 13, 2020 at 10:25:43AM +0000, Mel Gorman wrote:
> On Fri, Nov 13, 2020 at 12:01:21AM +0200, Jarkko Sakkinen wrote:
> > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > 
> > Background
> > ==========
> > 
> > 1. SGX enclave pages are populated with data by copying from normal memory
> >    via ioctl() (SGX_IOC_ENCLAVE_ADD_PAGES), which will be added later in
> >    this series.
> > 2. It is desirable to be able to restrict those normal memory data sources.
> >    For instance, to ensure that the source data is executable before
> >    copying data to an executable enclave page.
> > 3. Enclave page permissions are dynamic (just like normal permissions) and
> >    can be adjusted at runtime with mprotect().
> > 
> > This creates a problem because the original data source may have long since
> > vanished at the time when enclave page permissions are established (mmap()
> > or mprotect()).
> > 
> > The solution (elsewhere in this series) is to force enclaves creators to
> > declare their paging permission *intent* up front to the ioctl().  This
> > intent can be immediately compared to the source data???s mapping and
> > rejected if necessary.
> > 
> > The ???intent??? is also stashed off for later comparison with enclave
> > PTEs. This ensures that any future mmap()/mprotect() operations
> > performed by the enclave creator or done on behalf of the enclave
> > can be compared with the earlier declared permissions.
> > 
> > Problem
> > =======
> > 
> > There is an existing mmap() hook which allows SGX to perform this
> > permission comparison at mmap() time.  However, there is no corresponding
> > ->mprotect() hook.
> > 
> > Solution
> > ========
> > 
> > Add a vm_ops->mprotect() hook so that mprotect() operations which are
> > inconsistent with any page's stashed intent can be rejected by the driver.
> > 
> > Cc: linux-mm@...ck.org
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: Mel Gorman <mgorman@...hsingularity.net>
> > Acked-by: Jethro Beekman <jethro@...tanix.com> # v40
> > Acked-by: Dave Hansen <dave.hansen@...el.com> # v40
> > # Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Co-developed-by: Jarkko Sakkinen <jarkko@...nel.org>
> > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> 
> Acked-by: Mel Gorman <mgorman@...hsingularity.net>

Thank you.

/Jarkko