Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct vm_operations_struct

[Mel Gorman]

On Fri, Nov 13, 2020 at 12:01:21AM +0200, Jarkko Sakkinen wrote:
> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> 
> 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@xxxxxxxxx
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Acked-by: Jethro Beekman <jethro@xxxxxxxxxxxx> # v40
> Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx> # v40
> # Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Co-developed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

-- 
Mel Gorman
SUSE Labs