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

From: Christophe Leroy
Date: Tue Feb 19 2019 - 13:03:44 EST

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

Why do we need to disable branch profiling now?

Recommended by Andrey, see

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/ b/arch/powerpc/kernel/
index 667df97d2595..da6bb16e0876 100644
--- a/arch/powerpc/kernel/
+++ b/arch/powerpc/kernel/
@@ -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$" ?


+if [ $? -eq 0 ]
+ MEMFCT="__memcpy __memset"
+ MEMFCT="memcpy memset"


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

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
+#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.