On Wed, 28 Oct 2020 at 09:04, Ard Biesheuvel <a...@kernel.org> wrote: > > Commit 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot") > introduced a couple of uses of __attribute__((optimize)) with function > scope, to disable the stack protector in some early boot code. > > Unfortunately, and this is documented in the GCC man pages [0], overriding > function attributes for optimization is broken, and is only supported for > debug scenarios, not for production: the problem appears to be that > setting GCC -f flags using this method will cause it to forget about some > or all other optimization settings that have been applied. > > So the only safe way to disable the stack protector is to disable it for > the entire source file. > > [0] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html > > Cc: Michael Ellerman <m...@ellerman.id.au> > Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org> > Cc: Paul Mackerras <pau...@samba.org> > Cc: Nick Desaulniers <ndesaulni...@google.com> > Cc: Arvind Sankar <nived...@alum.mit.edu> > Cc: Randy Dunlap <rdun...@infradead.org> > Cc: Josh Poimboeuf <jpoim...@redhat.com> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Alexei Starovoitov <a...@kernel.org> > Cc: Daniel Borkmann <dan...@iogearbox.net> > Cc: Peter Zijlstra (Intel) <pet...@infradead.org> > Cc: Geert Uytterhoeven <ge...@linux-m68k.org> > Cc: Kees Cook <keesc...@chromium.org> > Fixes: 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot") > Signed-off-by: Ard Biesheuvel <a...@kernel.org> > --- > Related discussion here: > https://lore.kernel.org/lkml/CAMuHMdUg0WJHEcq6to0-eODpXPOywLot6UD2=gfhpzoj_hc...@mail.gmail.com/ > > TL;DR using __attribute__((optimize("-fno-gcse"))) in the BPF interpreter > causes the compiler to forget about -fno-asynchronous-unwind-tables passed > on the command line, resulting in unexpected .eh_frame sections in vmlinux. > > arch/powerpc/kernel/Makefile | 3 +++ > arch/powerpc/kernel/paca.c | 2 +- > arch/powerpc/kernel/setup.h | 6 ------ > arch/powerpc/kernel/setup_64.c | 2 +- > 4 files changed, 5 insertions(+), 8 deletions(-) >
FYI i was notified by one of the robots that I missed one occurrence of __nostackprotector in arch/powerpc/kernel/paca.c Let me know if I need to resend. > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile > index bf0bf1b900d2..fe2ef598e2ea 100644 > --- a/arch/powerpc/kernel/Makefile > +++ b/arch/powerpc/kernel/Makefile > @@ -173,6 +173,9 @@ KCOV_INSTRUMENT_cputable.o := n > KCOV_INSTRUMENT_setup_64.o := n > KCOV_INSTRUMENT_paca.o := n > > +CFLAGS_setup_64.o += -fno-stack-protector > +CFLAGS_paca.o += -fno-stack-protector > + > extra-$(CONFIG_PPC_FPU) += fpu.o > extra-$(CONFIG_ALTIVEC) += vector.o > extra-$(CONFIG_PPC64) += entry_64.o > diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c > index 0ad15768d762..fe70834d7283 100644 > --- a/arch/powerpc/kernel/paca.c > +++ b/arch/powerpc/kernel/paca.c > @@ -208,7 +208,7 @@ static struct rtas_args * __init new_rtas_args(int cpu, > unsigned long limit) > struct paca_struct **paca_ptrs __read_mostly; > EXPORT_SYMBOL(paca_ptrs); > > -void __init __nostackprotector initialise_paca(struct paca_struct *new_paca, > int cpu) > +void __init initialise_paca(struct paca_struct *new_paca, int cpu) > { > #ifdef CONFIG_PPC_PSERIES > new_paca->lppaca_ptr = NULL; > diff --git a/arch/powerpc/kernel/setup.h b/arch/powerpc/kernel/setup.h > index 2ec835574cc9..2dd0d9cb5a20 100644 > --- a/arch/powerpc/kernel/setup.h > +++ b/arch/powerpc/kernel/setup.h > @@ -8,12 +8,6 @@ > #ifndef __ARCH_POWERPC_KERNEL_SETUP_H > #define __ARCH_POWERPC_KERNEL_SETUP_H > > -#ifdef CONFIG_CC_IS_CLANG > -#define __nostackprotector > -#else > -#define __nostackprotector > __attribute__((__optimize__("no-stack-protector"))) > -#endif > - > void initialize_cache_info(void); > void irqstack_early_init(void); > > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c > index bb9cab3641d7..da447a62ea1e 100644 > --- a/arch/powerpc/kernel/setup_64.c > +++ b/arch/powerpc/kernel/setup_64.c > @@ -283,7 +283,7 @@ void __init record_spr_defaults(void) > * device-tree is not accessible via normal means at this point. > */ > > -void __init __nostackprotector early_setup(unsigned long dt_ptr) > +void __init early_setup(unsigned long dt_ptr) > { > static __initdata struct paca_struct boot_paca; > > -- > 2.17.1 >