Re: [PATCH v5 3/3] powerpc/32: Add KASAN support

[Christophe Leroy]

Le 18/02/2019 Ã 10:27, Michael Ellerman a ÃcritÂ:
> Christophe Leroy <christophe.leroy@xxxxxx> writes:
>
> > diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
> > index e0637730a8e7..dba2c1038363 100644
> > --- a/arch/powerpc/include/asm/ppc_asm.h
> > +++ b/arch/powerpc/include/asm/ppc_asm.h
> > @@ -251,6 +251,10 @@ GLUE(.,name):
> >   
> >   #define _GLOBAL_TOC(name) _GLOBAL(name)
> >   
> > +#define KASAN_OVERRIDE(x, y) \
> > +	.weak x;	     \
> > +	.set x, y
> > +
>
> Can you add a comment describing what that does and why?

It's gone. Hope the new approach is more clear. It's now in a dedicated 
patch.

> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index 879b36602748..fc4c42262694 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -16,8 +16,9 @@ CFLAGS_prom_init.o      += -fPIC
> >   CFLAGS_btext.o		+= -fPIC
> >   endif
> >   
> > -CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> > -CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> > +CFLAGS_early_32.o += -DDISABLE_BRANCH_PROFILING
> > +CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) -DDISABLE_BRANCH_PROFILING
> > +CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) -DDISABLE_BRANCH_PROFILING
>
> Why do we need to disable branch profiling now?

Recommended by Andrey, see https://patchwork.ozlabs.org/patch/1023887/

Maybe it should be only when KASAN is active ? For prom_init it should 
probably be all the time, for the others I don't know. Can't remember 
why I did it that way.

> I'd probably be happier if all the CFLAGS changes were done in a leadup
> patch to make them more obvious.

Oops, I forgot to read your mail entirely before sending out v6. Indeed 
I only read first part. Anyway, that's probably not the last run.

> > diff --git a/arch/powerpc/kernel/prom_init_check.sh b/arch/powerpc/kernel/prom_init_check.sh
> > index 667df97d2595..da6bb16e0876 100644
> > --- a/arch/powerpc/kernel/prom_init_check.sh
> > +++ b/arch/powerpc/kernel/prom_init_check.sh
> > @@ -16,8 +16,16 @@
> >   # If you really need to reference something from prom_init.o add
> >   # it to the list below:
> >   
> > +grep CONFIG_KASAN=y .config >/dev/null
>
> Just to be safe "^CONFIG_KASAN=y$" ?

ok

> > +if [ $? -eq 0 ]
> > +then
> > +	MEMFCT="__memcpy __memset"
> > +else
> > +	MEMFCT="memcpy memset"
> > +fi
>
> MEM_FUNCS ?

Yes, I change it now before I forget.

> > diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> > index 3bf9fc6fd36c..ce8d4a9f810a 100644
> > --- a/arch/powerpc/lib/Makefile
> > +++ b/arch/powerpc/lib/Makefile
> > @@ -8,6 +8,14 @@ ccflags-$(CONFIG_PPC64)	:= $(NO_MINIMAL_TOC)
> >   CFLAGS_REMOVE_code-patching.o = $(CC_FLAGS_FTRACE)
> >   CFLAGS_REMOVE_feature-fixups.o = $(CC_FLAGS_FTRACE)
> >   
> > +KASAN_SANITIZE_code-patching.o := n
> > +KASAN_SANITIZE_feature-fixups.o := n
> > +
> > +ifdef CONFIG_KASAN
> > +CFLAGS_code-patching.o += -DDISABLE_BRANCH_PROFILING
> > +CFLAGS_feature-fixups.o += -DDISABLE_BRANCH_PROFILING
> > +endif
>
> There's that branch profiling again, though here it's only if KASAN is enabled.
>
> > diff --git a/arch/powerpc/mm/kasan_init.c b/arch/powerpc/mm/kasan_init.c
> > new file mode 100644
> > index 000000000000..bd8e0a263e12
> > --- /dev/null
> > +++ b/arch/powerpc/mm/kasan_init.c
> > @@ -0,0 +1,114 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#define DISABLE_BRANCH_PROFILING
> > +
> > +#include <linux/kasan.h>
> > +#include <linux/printk.h>
> > +#include <linux/memblock.h>
> > +#include <linux/sched/task.h>
> > +#include <asm/pgalloc.h>
> > +
> > +void __init kasan_early_init(void)
> > +{
> > +	unsigned long addr = KASAN_SHADOW_START;
> > +	unsigned long end = KASAN_SHADOW_END;
> > +	unsigned long next;
> > +	pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(addr), addr), addr);
>
> Can none of those fail?

map_kernel_page() in pgtable_32.c does exactly the same.

pud_offset() and pmd_offset() are no-ops and only serve as type 
modifiers, so pmd will get the value returned by pgd_offset_k() which 
should always be valid unless init_mm->pgd is bad.

Christophe

> cheers