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

[Uladzislau Rezki]

On Wed, Jul 16, 2025 at 05:23:28PM +0200, Marco Elver wrote:
> 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@xxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> Cc: Yunseong Kim <ysk@xxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> ---
>  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
> 
Acked-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>

--
Uladzislau Rezki