On Tue, Jun 27, 2017 at 11:21:17AM -0700, Florian Fainelli wrote:

On 06/27/2017 10:38 AM, Mark Rutland wrote:

quoted

On Mon, Jun 26, 2017 at 03:32:42PM -0700, Florian Fainelli wrote:

quoted

Now that ARM64 also has a fncpy() implementation, allow selection
SRAM_EXEC for ARM64 as well.

Signed-off-by: Florian Fainelli <redacted>

Sorr,y but I must NAK this patch.

As mentioned on prior threads regarding fncpy, I do not think it makes
sense to enable this for arm64. The only use-cases that have been
described so far for this are power-management stuff that should live in
PSCI or other secure FW, and have no place in the kernel on arm64

This is a valid reason, but this is only one use case presented, the
only thing is that we need to make sure, as patch reviewers and you guys
as architecture maintainers, that this is not used as a means to bypass
PSCI for suspend/resume operation, which I now agree with.

Still, the general use case remains: you have a piece of addressable
memory which can be used to allocate space from and relocate code to be
it for security, performance, predictability, isolation, or anything,
and that should be possible given standard kernel facilities offered by
the SRAM driver.

While I agree that these are *theoretically* possible use cases, they
aren't *real* cases today. 

If someone comes by with code that needs this (which doesn't fall into
one of those NAK'd cases above), then I'm happy for this to be enabled
for that feature.

Until such time, I see no reason to enable this. Given it comes with
strong the potential for abuse, I'd rather it remained disabled.

quoted

quoted

There are no other users of this functionality, and until there are, I

see no reason to enable this, and risk a proliferation of unnecessary
platform-specific code.

It should be possible to #ifdef-ise the relevant callers of this such
that they can be built on arm64 without using fncpy or sram_exec
functionality. AFAICT, there are no users on arm64 introduced by this
series.

I sent this patch accidentally as part of this patch series anyway, so
if you want to keep the discussion alive, reply here:

https://patchwork.kernel.org/patch/9793745/

That appears to be v2 of the series, and there's a v3 afterwards, so
I've replied on v3.

Thanks,
Mark.
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