[Buildroot] [PATCH v2 01/28] boot/arm-trusted-firmware: option to disable stack protection

[Thomas Petazzoni]

Hello,

On Thu, 10 Jun 2021 01:03:56 +0300
Sergey Matyukevich <geomatsi at gmail.com> wrote:

> > It's a bit annoying that we have to tell TF-A about this. If TF-A
> > doesn't implement plat_get_stack_protector_canary() for a certain
> > platform, why does it try to enable SSP ? It feels like something that
> > should be fixed in TF-A.  
> 
> TF-A does not attempt to enable those protection checks. This is
> controlled by its ENABLE_STACK_PROTECTOR build flag, which default
> value is 'none'. This is Buildroot who tries to enable TF-A stack
> protection checks depending on BR2_SSP_* toolchain features only:
> see arm-trusted-firmware.mk.

I think:

ifeq ($(BR2_SSP_REGULAR),y)
ARM_TRUSTED_FIRMWARE_MAKE_OPTS += ENABLE_STACK_PROTECTOR=default
else ifeq ($(BR2_SSP_STRONG),y)
ARM_TRUSTED_FIRMWARE_MAKE_OPTS += ENABLE_STACK_PROTECTOR=strong
else ifeq ($(BR2_SSP_ALL),y)
ARM_TRUSTED_FIRMWARE_MAKE_OPTS += ENABLE_STACK_PROTECTOR=all
endif

is probably not great. BR2_SSP_* should really only affect user-space
code, IMO. For bare-metal/bootloader code, handling SSP really requires
special support, so we should probably not force it.

That being said, it's a bit weird for TF-A to provide that
ENABLE_STACK_PROTECTOR option in a way that doesn't build/work on all
platforms.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com