linux-kernel - Re: Linux 4.9.93

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Date:   Mon, 9 Apr 2018 10:55:34 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     20180408150840.GA16019@...ah.com
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        will.deacon@....com, dan.rue@...aro.org
Subject: Re: Linux 4.9.93

On Mon, Apr 09, 2018 at 06:05:34PM +0900, Jean-Baptiste Theou wrote:
> Hi,

Hi,

> After this patchset, a kernel built with CFI fails. Disabling
> UNMAP_KERNEL_AT_EL0 fix the issue obviously.
> 
> Wondering if there is one of the test suite used on the review
> patchset that covers the CFI usecase.

IIUC, you're saying that after my v4.9.y meltdown backport, your own
backport of an out-of-tree patchset does not function.

There's no support for CFI in upsteam (at least as of v4.16), nor in
v4.9.93. I have no idea as to how KPTI interacts with an out-of-tree
patchset, so could you elaborate on the issue?

I've not seen any CFI patches on the linux-arm-kernel mailing list, so
it's not clear to me how this interacts with KPTI.

Which patches do you have applied that implement CFI? Which compiler are
you using?

[...]

> [    0.282196] kernel BUG at kernel/cfi.c:32!

This file doesn't exit in v4.9.93...

> [    0.282230] CPU: 2 PID: 25 Comm: migration/2 Not tainted 4.9.93-perf+ #39

... and here I see you have local changes applied.

It would be best if you tried to get CFI supported upstream before
trying to backport it. That would be best discussed on the
linux-arm-kernel mailing list.

Thanks,
Mark.