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

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Message-ID: <20170517134734.GA10818@atomide.com>
Date:   Wed, 17 May 2017 06:47:35 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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

* Russell King - ARM Linux <linux@...linux.org.uk> [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@...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.

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.

Regards,

Tony