[Devel] [PATCH 1/4] kasan: update reported bug types for not user nor kernel memory accesses

[Andrey Ryabinin]

From: Andrey Konovalov <andreyknvl at google.com>

Each access with address lower than kasan_shadow_to_mem(KASAN_SHADOW_START)
is reported as user-memory-access. This is not always true, the accessed
address might not be in user space. Fix this by reporting such accesses as
null-ptr-derefs or wild-memory-accesses.

There's another reason for this change. For userspace ASan we have a bunch
of systems that analyze error types for the purpose of classification
and deduplication. Sooner of later we will write them to KASAN as well.
Then clearly and explicitly stated error types will bring value.

https://jira.sw.ru/browse/PSBM-39339

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
Signed-off-by: Andrey Ryabinin <aryabinin at odin.com>
---
 mm/kasan/kasan.c  |  8 +-------
 mm/kasan/kasan.h  |  3 ---
 mm/kasan/report.c | 45 +++++++++++++++++++++++----------------------
 3 files changed, 24 insertions(+), 32 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 6c513a6..d6798bc 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -236,18 +236,12 @@ static __always_inline bool memory_is_poisoned(unsigned long addr, size_t size)
 static __always_inline void check_memory_region(unsigned long addr,
 						size_t size, bool write)
 {
-	struct kasan_access_info info;
-
 	if (unlikely(size == 0))
 		return;
 
 	if (unlikely((void *)addr <
 		kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
-		info.access_addr = (void *)addr;
-		info.access_size = size;
-		info.is_write = write;
-		info.ip = _RET_IP_;
-		kasan_report_user_access(&info);
+		kasan_report(addr, size, write, _RET_IP_);
 		return;
 	}
 
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 4986b0a..14cdff3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -55,9 +55,6 @@ struct kasan_global {
 #endif
 };
 
-void kasan_report_error(struct kasan_access_info *info);
-void kasan_report_user_access(struct kasan_access_info *info);
-
 static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 {
 	return (void *)(((unsigned long)shadow_addr - KASAN_SHADOW_OFFSET)
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 680ceed..ad69bac 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -182,34 +182,34 @@ static void print_shadow_for_address(const void *addr)
 
 static DEFINE_SPINLOCK(report_lock);
 
-void kasan_report_error(struct kasan_access_info *info)
+static void kasan_report_error(struct kasan_access_info *info)
 {
 	unsigned long flags;
+	const char *bug_type;
 
 	spin_lock_irqsave(&report_lock, flags);
 	pr_err("================================="
 		"=================================\n");
-	print_error_description(info);
-	print_address_description(info);
-	print_shadow_for_address(info->first_bad_addr);
-	pr_err("================================="
-		"=================================\n");
-	spin_unlock_irqrestore(&report_lock, flags);
-}
-
-void kasan_report_user_access(struct kasan_access_info *info)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&report_lock, flags);
-	pr_err("================================="
-		"=================================\n");
-	pr_err("BUG: KASan: user-memory-access on address %p\n",
-		info->access_addr);
-	pr_err("%s of size %zu by task %s/%d\n",
-		info->is_write ? "Write" : "Read",
-		info->access_size, current->comm, task_pid_nr(current));
-	dump_stack();
+	if (info->access_addr <
+			kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) {
+		if ((unsigned long)info->access_addr < PAGE_SIZE)
+			bug_type = "null-ptr-deref";
+		else if ((unsigned long)info->access_addr < TASK_SIZE)
+			bug_type = "user-memory-access";
+		else
+			bug_type = "wild-memory-access";
+		pr_err("BUG: KASan: %s on address %p\n",
+			bug_type, info->access_addr);
+		pr_err("%s of size %zu by task %s/%d\n",
+			info->is_write ? "Write" : "Read",
+			info->access_size, current->comm,
+			task_pid_nr(current));
+		dump_stack();
+	} else {
+		print_error_description(info);
+		print_address_description(info);
+		print_shadow_for_address(info->first_bad_addr);
+	}
 	pr_err("================================="
 		"=================================\n");
 	spin_unlock_irqrestore(&report_lock, flags);
@@ -227,6 +227,7 @@ void kasan_report(unsigned long addr, size_t size,
 	info.access_size = size;
 	info.is_write = is_write;
 	info.ip = ip;
+
 	kasan_report_error(&info);
 }
 
-- 
2.4.6