Re: [PATCH v2] kernel/memremap, kasan: Make ZONE_DEVICE with work with KASAN

From: Andrew Morton
Date: Fri Jun 29 2018 - 22:33:13 EST


On Fri, 29 Jun 2018 19:49:32 +0300 Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:

> KASAN learns about hot added memory via the memory hotplug notifier.
> The devm_memremap_pages() intentionally skips calling memory hotplug
> notifiers.

Why does it do that?

> So KASAN doesn't know anything about new memory added
> by devm_memremap_pages(). This causes to crash when KASAN tries to
> access non-existent shadow memory:
>
> BUG: unable to handle kernel paging request at ffffed0078000000
> RIP: 0010:check_memory_region+0x82/0x1e0
> Call Trace:
> memcpy+0x1f/0x50
> pmem_do_bvec+0x163/0x720
> pmem_make_request+0x305/0xac0
> generic_make_request+0x54f/0xcf0
> submit_bio+0x9c/0x370
> submit_bh_wbc+0x4c7/0x700
> block_read_full_page+0x5ef/0x870
> do_read_cache_page+0x2b8/0xb30
> read_dev_sector+0xbd/0x3f0
> read_lba.isra.0+0x277/0x670
> efi_partition+0x41a/0x18f0
> check_partition+0x30d/0x5e9
> rescan_partitions+0x18c/0x840
> __blkdev_get+0x859/0x1060
> blkdev_get+0x23f/0x810
> __device_add_disk+0x9c8/0xde0
> pmem_attach_disk+0x9a8/0xf50
> nvdimm_bus_probe+0xf3/0x3c0
> driver_probe_device+0x493/0xbd0
> bus_for_each_drv+0x118/0x1b0
> __device_attach+0x1cd/0x2b0
> bus_probe_device+0x1ac/0x260
> device_add+0x90d/0x1380
> nd_async_device_register+0xe/0x50
> async_run_entry_fn+0xc3/0x5d0
> process_one_work+0xa0a/0x1810
> worker_thread+0x87/0xe80
> kthread+0x2d7/0x390
> ret_from_fork+0x3a/0x50
>
> Add kasan_add_zero_shadow()/kasan_remove_zero_shadow() - post mm_init()
> interface to map/unmap kasan_zero_page at requested virtual addresses.
> And use it to add/remove the shadow memory for hotpluged/unpluged
> device memory.
>
> Reported-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>

No cc:stable? Which kernel version(s) do you believe need the fix?

> include/linux/kasan.h | 13 ++-
> kernel/memremap.c | 10 ++
> mm/kasan/kasan_init.c | 316 +++++++++++++++++++++++++++++++++++++++++++++++---

It's a surprisingly large amount of ode to do something which KASAN
already does for hotplugged memory. How come?