[PATCH v2] kasan: also display registers for reports from HW exceptions

[Peter Collingbourne]

It is sometimes useful to know the values of the registers when a KASAN
report is generated. We can do this easily for reports that resulted from
a hardware exception by passing the struct pt_regs from the exception into
the report function; do so, but only in HW tags mode because registers
may have been corrupted during the check in other modes.

Signed-off-by: Peter Collingbourne <pcc at google.com>
---
Applies to -next.

v2:
- only do this in HW tags mode
- move pr_err to caller

 arch/arm64/mm/fault.c |  2 +-
 include/linux/kasan.h | 10 ++++++++++
 mm/kasan/kasan.h      |  1 +
 mm/kasan/report.c     | 30 +++++++++++++++++++++++-------
 4 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 5b391490e045..c4b91f5d8cc8 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -316,7 +316,7 @@ static void report_tag_fault(unsigned long addr, unsigned long esr,
 	 * find out access size.
 	 */
 	bool is_write = !!(esr & ESR_ELx_WNR);
-	kasan_report(addr, 0, is_write, regs->pc);
+	kasan_report_regs(addr, 0, is_write, regs);
 }
 #else
 /* Tag faults aren't enabled without CONFIG_KASAN_HW_TAGS. */
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index d811b3d7d2a1..381aea149353 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -353,6 +353,16 @@ static inline void *kasan_reset_tag(const void *addr)
 bool kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 
+/**
+ * kasan_report_regs - print a report about a bad memory access detected by KASAN
+ * @addr: address of the bad access
+ * @size: size of the bad access
+ * @is_write: whether the bad access is a write or a read
+ * @regs: register values at the point of the bad memory access
+ */
+bool kasan_report_regs(unsigned long addr, size_t size, bool is_write,
+		       struct pt_regs *regs);
+
 #else /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
 
 static inline void *kasan_reset_tag(const void *addr)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index abbcc1b0eec5..39772c21a8ae 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -175,6 +175,7 @@ struct kasan_report_info {
 	size_t access_size;
 	bool is_write;
 	unsigned long ip;
+	struct pt_regs *regs;
 
 	/* Filled in by the common reporting code. */
 	void *first_bad_addr;
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index df3602062bfd..be8dd97940c7 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -24,6 +24,7 @@
 #include <linux/types.h>
 #include <linux/kasan.h>
 #include <linux/module.h>
+#include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 #include <linux/uaccess.h>
 #include <trace/events/error_report.h>
@@ -281,9 +282,6 @@ static void print_address_description(void *addr, u8 tag,
 {
 	struct page *page = addr_to_page(addr);
 
-	dump_stack_lvl(KERN_ERR);
-	pr_err("\n");
-
 	if (info->cache && info->object) {
 		describe_object(addr, info);
 		pr_err("\n");
@@ -391,11 +389,15 @@ static void print_report(struct kasan_report_info *info)
 		kasan_print_tags(tag, info->first_bad_addr);
 	pr_err("\n");
 
+	if (info->regs)
+		show_regs(info->regs);
+	else
+		dump_stack_lvl(KERN_ERR);
+
 	if (addr_has_metadata(addr)) {
+		pr_err("\n");
 		print_address_description(addr, tag, info);
 		print_memory_metadata(info->first_bad_addr);
-	} else {
-		dump_stack_lvl(KERN_ERR);
 	}
 }
 
@@ -467,8 +469,8 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_ty
  * user_access_save/restore(): kasan_report_invalid_free() cannot be called
  * from a UACCESS region, and kasan_report_async() is not used on x86.
  */
-bool kasan_report(unsigned long addr, size_t size, bool is_write,
-			unsigned long ip)
+static bool __kasan_report(unsigned long addr, size_t size, bool is_write,
+			unsigned long ip, struct pt_regs *regs)
 {
 	bool ret = true;
 	void *ptr = (void *)addr;
@@ -489,6 +491,7 @@ bool kasan_report(unsigned long addr, size_t size, bool is_write,
 	info.access_size = size;
 	info.is_write = is_write;
 	info.ip = ip;
+	info.regs = regs;
 
 	complete_report_info(&info);
 
@@ -502,6 +505,19 @@ bool kasan_report(unsigned long addr, size_t size, bool is_write,
 	return ret;
 }
 
+bool kasan_report(unsigned long addr, size_t size, bool is_write,
+			unsigned long ip)
+{
+	return __kasan_report(addr, size, is_write, ip, NULL);
+}
+
+bool kasan_report_regs(unsigned long addr, size_t size, bool is_write,
+		       struct pt_regs *regs)
+{
+	return __kasan_report(addr, size, is_write, instruction_pointer(regs),
+			      regs);
+}
+
 #ifdef CONFIG_KASAN_HW_TAGS
 void kasan_report_async(void)
 {
-- 
2.37.3.998.g577e59143f-goog