[PATCH] kasan: use vmalloc_dump_obj() for vmalloc error reports

[Marco Elver <elver@google.com>]

Since 6ee9b3d84775 ("kasan: remove kasan_find_vm_area() to prevent
possible deadlock"), more detailed info about the vmalloc mapping and
the origin was dropped due to potential deadlocks.

While fixing the deadlock is necessary, that patch was too quick in
killing an otherwise useful feature, and did no due-diligence in
understanding if an alternative option is available.

Restore printing more helpful vmalloc allocation info in KASAN reports
with the help of vmalloc_dump_obj(). Example report:

| BUG: KASAN: vmalloc-out-of-bounds in vmalloc_oob+0x4c9/0x610
| Read of size 1 at addr ffffc900002fd7f3 by task kunit_try_catch/493
|
| CPU: [...]
| Call Trace:
|  <TASK>
|  dump_stack_lvl+0xa8/0xf0
|  print_report+0x17e/0x810
|  kasan_report+0x155/0x190
|  vmalloc_oob+0x4c9/0x610
|  [...]
|
| The buggy address belongs to a 1-page vmalloc region starting at 0xffffc900002fd000 allocated at vmalloc_oob+0x36/0x610
| The buggy address belongs to the physical page:
| page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x126364
| flags: 0x200000000000000(node=0|zone=2)
| raw: 0200000000000000 0000000000000000 dead000000000122 0000000000000000
| raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
| page dumped because: kasan: bad access detected
|
| [..]

Fixes: 6ee9b3d84775 ("kasan: remove kasan_find_vm_area() to prevent possible deadlock")
Suggested-by: Uladzislau Rezki <urezki@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Yeoreum Yun <yeoreum.yun@arm.com>
Cc: Yunseong Kim <ysk@kzalloc.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
---
 mm/kasan/report.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index b0877035491f..62c01b4527eb 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -399,7 +399,9 @@ static void print_address_description(void *addr, u8 tag,
 	}
 
 	if (is_vmalloc_addr(addr)) {
-		pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n", addr);
+		pr_err("The buggy address belongs to a");
+		if (!vmalloc_dump_obj(addr))
+			pr_cont(" vmalloc virtual mapping\n");
 		page = vmalloc_to_page(addr);
 	}
 
-- 
2.50.0.727.gbf7dc18ff4-goog