[RFC WIP PATCH 2/3] kasan: allow architectures to manage the memory-to-shadow mapping

[Christophe Leroy]

From: Daniel Axtens <dja at axtens.net>

Currently, shadow addresses are always addr >> shift + offset.
However, for powerpc, the virtual address space is fragmented in
ways that make this simple scheme impractical.

Allow architectures to override:
 - kasan_shadow_to_mem
 - kasan_mem_to_shadow
 - addr_has_shadow

Rename addr_has_shadow to kasan_addr_has_shadow as if it is
overridden it will be available in more places, increasing the
risk of collisions.

If architectures do not #define their own versions, the generic
code will continue to run as usual.

Signed-off-by: Daniel Axtens <dja at axtens.net>
Reviewed-by: Dmitry Vyukov <dvyukov at google.com>
---
 include/linux/kasan.h     | 2 ++
 mm/kasan/generic.c        | 2 +-
 mm/kasan/generic_report.c | 2 +-
 mm/kasan/kasan.h          | 6 +++++-
 mm/kasan/report.c         | 6 +++---
 mm/kasan/tags.c           | 2 +-
 6 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b91c40af9f31..a630d53f1a36 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -27,11 +27,13 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
 int kasan_populate_early_shadow(const void *shadow_start,
 				const void *shadow_end);
 
+#ifndef kasan_mem_to_shadow
 static inline void *kasan_mem_to_shadow(const void *addr)
 {
 	return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
 		+ KASAN_SHADOW_OFFSET;
 }
+#endif
 
 /* Enable reporting bugs after kasan_disable_current() */
 extern void kasan_enable_current(void);
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 08cbc7ed8953..6c6c30643d51 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -176,7 +176,7 @@ static __always_inline void check_memory_region_inline(unsigned long addr,
 	if (unlikely(size == 0))
 		return;
 
-	if (unlikely(!addr_has_shadow((void *)addr))) {
+	if (unlikely(!kasan_addr_has_shadow((void *)addr))) {
 		kasan_report(addr, size, write, ret_ip);
 		return;
 	}
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index 5e12035888f2..854f4de1fe10 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -110,7 +110,7 @@ static const char *get_wild_bug_type(struct kasan_access_info *info)
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
-	if (addr_has_shadow(info->access_addr))
+	if (kasan_addr_has_shadow(info->access_addr))
 		return get_shadow_bug_type(info);
 	return get_wild_bug_type(info);
 }
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index ea51b2d898ec..57ec24cf7bd1 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -111,16 +111,20 @@ struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
 struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
 					const void *object);
 
+#ifndef kasan_shadow_to_mem
 static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 {
 	return (void *)(((unsigned long)shadow_addr - KASAN_SHADOW_OFFSET)
 		<< KASAN_SHADOW_SCALE_SHIFT);
 }
+#endif
 
-static inline bool addr_has_shadow(const void *addr)
+#ifndef kasan_addr_has_shadow
+static inline bool kasan_addr_has_shadow(const void *addr)
 {
 	return (addr >= kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
 }
+#endif
 
 void kasan_poison_shadow(const void *address, size_t size, u8 value);
 
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index ca9418fe9232..bc3355ee2dd0 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -298,7 +298,7 @@ void kasan_report(unsigned long addr, size_t size,
 	untagged_addr = reset_tag(tagged_addr);
 
 	info.access_addr = tagged_addr;
-	if (addr_has_shadow(untagged_addr))
+	if (kasan_addr_has_shadow(untagged_addr))
 		info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 	else
 		info.first_bad_addr = untagged_addr;
@@ -309,11 +309,11 @@ void kasan_report(unsigned long addr, size_t size,
 	start_report(&flags);
 
 	print_error_description(&info);
-	if (addr_has_shadow(untagged_addr))
+	if (kasan_addr_has_shadow(untagged_addr))
 		print_tags(get_tag(tagged_addr), info.first_bad_addr);
 	pr_err("\n");
 
-	if (addr_has_shadow(untagged_addr)) {
+	if (kasan_addr_has_shadow(untagged_addr)) {
 		print_address_description(untagged_addr);
 		pr_err("\n");
 		print_shadow_for_address(info.first_bad_addr);
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index bc759f8f1c67..cdefd0fe1f5d 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -109,7 +109,7 @@ void check_memory_region(unsigned long addr, size_t size, bool write,
 		return;
 
 	untagged_addr = reset_tag((const void *)addr);
-	if (unlikely(!addr_has_shadow(untagged_addr))) {
+	if (unlikely(!kasan_addr_has_shadow(untagged_addr))) {
 		kasan_report(addr, size, write, ret_ip);
 		return;
 	}
-- 
2.13.3