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

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Date:   Wed, 17 May 2017 12:43:07 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Tony Lindgren <tony@...mide.com>, Dave Gerlach <d-gerlach@...com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, Shawn Guo <shawnguo@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Keerthy J <j-keerthy@...com>
Subject: Re: [PATCH v2] misc: sram-exec: Use aligned fncpy instead of memcpy

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@...linux.org.uk> [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@...com>
> > > 
> > > Looks a lot saner, thanks.  It's just a bit sad that we lose the type
> > > checking.
> > > 
> > > Acked-by: Russell King <rmk+kernel@...linux.org.uk>
> > 
> > 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.

-- 
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