[RFC PATCH 3/5] kasan: allow architectures to provide an outline readiness check

[Daniel Axtens <dja@axtens.net>]

In powerpc (as I understand it), we spend a lot of time in boot
running in real mode before MMU paging is initalised. During
this time we call a lot of generic code, including printk(). If
we try to access the shadow region during this time, things fail.

My attempts to move early init before the first printk have not
been successful. (Both previous RFCs for ppc64 - by 2 different
people - have needed this trick too!)

So, allow architectures to define a check_return_arch_not_ready()
hook that bails out of check_memory_region_inline() unless the
arch has done all of the init.

Link: https://lore.kernel.org/patchwork/patch/592820/ # ppc64 hash series
Link: https://patchwork.ozlabs.org/patch/795211/      # ppc radix series
Originally-by: Balbir Singh <bsingharora@gmail.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 include/linux/kasan.h | 4 ++++
 mm/kasan/generic.c    | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index f6261840f94c..83edc5e2b6a0 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -14,6 +14,10 @@ struct task_struct;
 #include <asm/kasan.h>
 #include <asm/pgtable.h>
 
+#ifndef check_return_arch_not_ready
+#define check_return_arch_not_ready()	do { } while (0)
+#endif
+
 extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
 extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
 extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index bafa2f986660..4c18bbd09a20 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -170,6 +170,8 @@ static __always_inline void check_memory_region_inline(unsigned long addr,
 						size_t size, bool write,
 						unsigned long ret_ip)
 {
+	check_return_arch_not_ready();
+
 	if (unlikely(size == 0))
 		return;
 
-- 
2.19.1