Subject: Re: [PATCH] security: do not enable CONFIG_GCC_PLUGINS by default

From: Kees Cook <[email-masked]>
Date: Fri, 14 Jun 2019 20:08:42 -0700

On Fri, Jun 14, 2019 at 06:05:19PM +0200, Jann Horn wrote:
> On Fri, Jun 14, 2019 at 5:10 PM Denis 'GNUtoo' Carikli
> <[email-masked]> wrote:
> > Booting was broken by the following commit:
> >   9f671e58159a ("security: Create "kernel hardening" config area")
> 
> I don't think GCC_PLUGINS alone is supposed to generate any code? It
> just makes it possible to enable a bunch of other kconfig flags that
> can generate code.
> 
> STACKPROTECTOR_PER_TASK defaults to y and depends on GCC_PLUGINS, so
> is that perhaps what broke? Can you try whether disabling just that
> works for you?

Yes, this has come up before: the option you want to disable is as Jann
mentions: CONFIG_STACKPROTECTOR_PER_TASK.

> My guess is that maybe there is some early boot code that needs to
> have the stack protector disabled, or something like that.

Right, though I'm not sure what portion would be specific to that
device. You can turn off SSP on a per-file basis with:

CFLAGS_target.o += $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)

or per-Makefile, as in arch/arm/boot/compressed/Makefile.

-- 
Kees Cook

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