Re: linux-next: build failure after merge of the kspp tree

[Kees Cook <keescook@google.com>]

On Fri, Jul 27, 2018 at 6:27 AM, Will Deacon <will.deacon@arm.com> wrote:
> On Fri, Jul 27, 2018 at 02:01:06PM +0100, Will Deacon wrote:
>> On Fri, Jul 27, 2018 at 01:55:22PM +0100, Will Deacon wrote:
>> > On Fri, Jul 27, 2018 at 08:55:11PM +1000, Stephen Rothwell wrote:
>> > > On Fri, 27 Jul 2018 19:06:47 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>> > > >
>> > > > On Fri, 27 Jul 2018 19:02:07 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>> > > > >
>> > > > > After merging the kspp tree, today's linux-next build (x86_64
>> > > > > allmodconfig) failed like this:
>> > > > >
>> > > > > cc1: error: plugin stackleak_plugin should be specified before -fplugin-arg-stackleak_plugin-disable in the command line
>> > > > >
>> > > > > Maybe caused by commit
>> > > > >
>> > > > >   a8b9eaddb9c0 ("gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack")
>> > > > >
>> > > > > I have used the kspp tree from next-20180726 for today.
>> > > >
>> > > > Well, that obviously didn't work since the tree hasn't changed for a
>> > > > few days.
>> > > >
>> > > > I can't see what has interacted to make this happen, so I have dropped
>> > > > the kspp tree for today.
>> > >
>> > > Actually, it may have been caused by commit
>> > >
>> > >   0b3e336601b8 ("arm64: Add support for STACKLEAK gcc plugin")
>> > >
>> > > from the arm64 tree.
>> >
>> > Thanks, Stephen. I managed to reproduce this by merging for-next/kspp from
>> > Kees's tree and for-next/core from the arm64 tree. The failure happens when
>> > building the EFI stub, so the commit you mention above is almost certainly
>> > the culprit.
>> >
>> > We build the stub with the following GCC invocation:
>> >
>> >  gcc -Wp,-MD,drivers/firmware/efi/libstub/.efi-stub-helper.o.d  -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/4.9/include -I./arch/x86/include -I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -mcmodel=small -m64 -D__KERNEL__ -O2 -fPIC -fno-strict-aliasing -mno-red-zone -mno-mmx -mno-sse -fshort-wchar -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY -ffreestanding -fno-stack-protector -fplugin-arg-stackleak_plugin-disable   -fno-builtin      -DKBUILD_BASENAME='"efi_stub_helper"' -DKBUILD_MODNAME='"efi_stub_helper"' -c -o drivers/firmware/efi/libstub/.tmp_efi-stub-helper.o drivers/firmware/efi/libstub/efi-stub-helper.c
>> >
>> > so given that we're not passing any -fplugin= option anyway (because we
>> > override KBUILD_CFLAGS for the stub), I don't understand why we need
>> > to the disable option at all.
>> >
>> > Laura?
>>
>> ... ah, but arm and arm64 inherit the old KBUILD_CFLAGS via the
>> cflags-$(CONFIG_ARM64) and cflags-$(CONFIG_ARM) definitions, so they
>> would be the places where we need to disable the plugin.
>
> i.e. something like the diff below.
>
> Will
>
> --->8
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 25dd2a14560d..f3700fe08908 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -11,9 +11,11 @@ cflags-$(CONFIG_X86)         += -m$(BITS) -D__KERNEL__ -O2 \
>                                    -fPIC -fno-strict-aliasing -mno-red-zone \
>                                    -mno-mmx -mno-sse -fshort-wchar
>
> -cflags-$(CONFIG_ARM64)         := $(subst -pg,,$(KBUILD_CFLAGS)) -fpie
> +cflags-$(CONFIG_ARM64)         := $(subst -pg,,$(KBUILD_CFLAGS)) -fpie \
> +                                  $(DISABLE_STACKLEAK_PLUGIN)
>  cflags-$(CONFIG_ARM)           := $(subst -pg,,$(KBUILD_CFLAGS)) \
> -                                  -fno-builtin -fpic -mno-single-pic-base
> +                                  -fno-builtin -fpic -mno-single-pic-base \
> +                                  $(DISABLE_STACKLEAK_PLUGIN)
>
>  cflags-$(CONFIG_EFI_ARMSTUB)   += -I$(srctree)/scripts/dtc/libfdt
>
> @@ -21,7 +23,6 @@ KBUILD_CFLAGS                 := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
>                                    -D__NO_FORTIFY \
>                                    $(call cc-option,-ffreestanding) \
>                                    $(call cc-option,-fno-stack-protector) \
> -                                  $(DISABLE_STACKLEAK_PLUGIN)
>
>  GCOV_PROFILE                   := n
>  KASAN_SANITIZE                 := n

Ah! Thanks for tracking this down!

-Kees

-- 
Kees Cook
Pixel Security