Re: [PATCH v2] misc: sram-exec: Use aligned fncpy instead of memcpy

[Dave Gerlach]

On 05/17/2017 08:47 AM, Tony Lindgren wrote:
> * Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> [170517 04:46]:
> > On Wed, May 17, 2017 at 11:13:17AM +0200, Greg Kroah-Hartman wrote:
> > > On Tue, May 16, 2017 at 09:01:27AM -0700, Tony Lindgren wrote:
> > > > * Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> [170503 11:58]:
> > > > > On Mon, Apr 10, 2017 at 09:52:47AM -0500, Dave Gerlach wrote:
> > > > > > Currently the sram-exec functionality, which allows allocation of
> > > > > > executable memory and provides an API to move code to it, is only
> > > > > > selected in configs for the ARM architecture. Based on commit
> > > > > > 5756e9dd0de6 ("ARM: 6640/1: Thumb-2: Symbol manipulation macros for
> > > > > > function body copying") simply copying a C function pointer address
> > > > > > using memcpy without consideration of alignment and Thumb is unsafe on
> > > > > > ARM platforms.
> > > > > >
> > > > > > The aforementioned patch introduces the fncpy macro which is a safe way
> > > > > > to copy executable code on ARM platforms, so let's make use of that here
> > > > > > rather than the unsafe plain memcpy that was previously used by
> > > > > > sram_exec_copy. Now sram_exec_copy will move the code to "dst" and
> > > > > > return an address that is guaranteed to be safely callable.
> > > > > >
> > > > > > In the future, architectures hoping to make use of the sram-exec
> > > > > > functionality must define an fncpy macro just as ARM has done to
> > > > > > guarantee or check for safe copying to executable memory before allowing
> > > > > > the arch to select CONFIG_SRAM_EXEC.
> > > > > >
> > > > > > Signed-off-by: Dave Gerlach <d-gerlach@xxxxxx>
> > > > >
> > > > > Looks a lot saner, thanks.  It's just a bit sad that we lose the type
> > > > > checking.
> > > > >
> > > > > Acked-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> > > >
> > > > Looks like this is still pending so I'll add it into
> > > > omap-for-v4.12/fixes so we can get this out of the way.
> > >
> > > It's a "fix"?  Looked to be a 4.13 issue, sorry for the delay, otherwise
> > > I would have queued it up earlier.
> >
> > Technically, it is a fix, but my greps for "sram_exec_copy" indicate
> > that the code does not yet have any in-tree users.  So I don't think
> > there's any urgency to picking this up, and I think no need to back
> > port to stable trees.
>
> OK fine, I'll drop it today from my fixes (and for-next) no problem.
> I did add a fixes tag to it which would then create confusion later
> on too with stable trees.
>
> Dave, probably best to resend the patch to Greg in few days with acks
> added and rebased against v4.12-rc1 because it won't apply without a
> merge because of the header changes.

Yes, there are no users yet. Was planning on resending this anyway, so I'll do 
that before I send my patches that make use of this.

Regards,
Dave

> Regards,
>
> Tony