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

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Date:   Thu, 5 Nov 2020 17:04:24 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
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>,
        Darren Kenny <darren.kenny@...cle.com>,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com,
        cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.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 v40 10/24] mm: Add 'mprotect' hook to struct
 vm_operations_struct

On Wed, Nov 04, 2020 at 04:54:16PM +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 me 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>
> Acked-by: Jethro Beekman <jethro@...tanix.com>
> Reviewed-by: Darren Kenny <darren.kenny@...cle.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
>  include/linux/mm.h | 3 +++
>  mm/mprotect.c      | 5 ++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)

This needs an ACK from an mm person.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette