Re: [PATCH] mm: fix possible OOB in numa_rebuild_large_mapping()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

Hi David and Baolin,

On 2024/6/7 18:37, David Hildenbrand wrote:
> On 07.06.24 12:32, Kefeng Wang wrote:
>> The large folio is mapped with folio size aligned virtual address during
>> the pagefault, eg, 'addr = ALIGN_DOWN(vmf->address, nr_pages * 
>> PAGE_SIZE)'
>> in do_anonymous_page(), but after the mremap(), the virtual address only
>> require PAGE_SIZE aligned, also pte is moved to new in 
>> move_page_tables(),
>> then traverse the new pte in numa_rebuild_large_mapping() will hint the
>> following issue,
>>
>>     Unable to handle kernel paging request at virtual address 
>> 00000a80c021a788
>>     Mem abort info:
>>       ESR = 0x0000000096000004
>>       EC = 0x25: DABT (current EL), IL = 32 bits
>>       SET = 0, FnV = 0
>>       EA = 0, S1PTW = 0
>>       FSC = 0x04: level 0 translation fault
>>     Data abort info:
>>       ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
>>       CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>>       GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>>     user pgtable: 4k pages, 48-bit VAs, pgdp=00002040341a6000
>>     [00000a80c021a788] pgd=0000000000000000, p4d=0000000000000000
>>     Internal error: Oops: 0000000096000004 [#1] SMP
>>     ...
>>     CPU: 76 PID: 15187 Comm: git Kdump: loaded Tainted: G        
>> W          6.10.0-rc2+ #209
>>     Hardware name: Huawei TaiShan 2280 V2/BC82AMDD, BIOS 1.79 08/21/2021
>>     pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>     pc : numa_rebuild_large_mapping+0x338/0x638
>>     lr : numa_rebuild_large_mapping+0x320/0x638
>>     sp : ffff8000b41c3b00
>>     x29: ffff8000b41c3b30 x28: ffff8000812a0000 x27: 00000000000a8000
>>     x26: 00000000000000a8 x25: 0010000000000001 x24: ffff20401c7170f0
>>     x23: 0000ffff33a1e000 x22: 0000ffff33a76000 x21: ffff20400869eca0
>>     x20: 0000ffff33976000 x19: 00000000000000a8 x18: ffffffffffffffff
>>     x17: 0000000000000000 x16: 0000000000000020 x15: ffff8000b41c36a8
>>     x14: 0000000000000000 x13: 205d373831353154 x12: 5b5d333331363732
>>     x11: 000000000011ff78 x10: 000000000011ff10 x9 : ffff800080273f30
>>     x8 : 000000320400869e x7 : c0000000ffffd87f x6 : 00000000001e6ba8
>>     x5 : ffff206f3fb5af88 x4 : 0000000000000000 x3 : 0000000000000000
>>     x2 : 0000000000000000 x1 : fffffdffc0000000 x0 : 00000a80c021a780
>>     Call trace:
>>      numa_rebuild_large_mapping+0x338/0x638
>>      do_numa_page+0x3e4/0x4e0
>>      handle_pte_fault+0x1bc/0x238
>>      __handle_mm_fault+0x20c/0x400
>>      handle_mm_fault+0xa8/0x288
>>      do_page_fault+0x124/0x498
>>      do_translation_fault+0x54/0x80
>>      do_mem_abort+0x4c/0xa8
>>      el0_da+0x40/0x110
>>      el0t_64_sync_handler+0xe4/0x158
>>      el0t_64_sync+0x188/0x190
> 
> Do you have an easy reproducer that we can use to reproduce+verify this 
> issue? The description above indicates to me that this should not be too 
> complicated to write :)
> 

Sorry for the late due to traditional Chinese festival, the issue is
easily reproduced when enable mTHP but drop the "align larger anonymous
mappings on THP boundaries" on arm64, here is the step,

   drop the align anon mapping on THP[Optional, but not very easy to 
reproduce]
   cd /sys/kernel/mm/transparent_hugepage/
   echo never  > hugepage-2048kB/never
   echo always > hugepage-1024kB/never  (other size could reproduce 
issue too)
   git clone root@127.0.0.1:/home/git/linux  (clone the local kernel repo)

and in numa_rebuild_large_mapping(), we hint some different errors, but
most are the bad access when

   if (pfn_folio(pte_pfn(ptent)) != folio)

The page is invalid, so guess the ptent/start_ptep is wrong when
traverse.