[PATCH] kasan: Add explicit preconditions to kasan_report()

[Vincenzo Frascino]

With the introduction of KASAN_HW_TAGS, kasan_report() dereferences
the address passed as a parameter.

Add a comment to make sure that the preconditions to the function are
explicitly clarified.

Note: An invalid address (e.g. NULL pointer address) passed to the
function when, KASAN_HW_TAGS is enabled, leads to a kernel panic.

Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Leon Romanovsky <leonro@xxxxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
 mm/kasan/report.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index c0fb21797550..2485b585004d 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write,
 	end_report(&flags);
 }
 
+/**
+ * kasan_report - report kasan fault details
+ * @addr: valid address of the allocation where the tag fault was detected
+ * @size: size of the allocation where the tag fault was detected
+ * @is_write: the instruction that caused the fault was a read or write?
+ * @ip: pointer to the instruction that cause the fault
+ *
+ * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences
+ * the address to access the tags, hence it must be valid at this point in
+ * order to not cause a kernel panic.
+ */
 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 			unsigned long ip)
 {
-- 
2.30.0