[PATCH 1/7] kasan: update reported bug types for not user nor kernel memory accesses

[Andrey Konovalov <andreyknvl@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.

Signed-off-by: Andrey Konovalov <andreyknvl@google.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 7b28e9c..035f268 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 c242adf..df794fa 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -54,9 +54,6 @@ 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 e07c94f..4d3551d 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);
 }
 
-- 
2.5.0.457.gab17608

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