Re: linux-next: not-present page at swap_vma_readahead()

[Qian Cai <cai@lca.pw>]

On Wed, Apr 15, 2020 at 10:01:53AM +0800, Huang, Ying wrote:
> Qian Cai <cai@lca.pw> writes:
> 
> >> On Apr 14, 2020, at 10:32 AM, Qian Cai <cai@lca.pw> wrote:
> >> 
> >> Fuzzers are unhappy. Thoughts?
> >
> > This is rather to reproduce. All the traces so far are from copy_from_user() to trigger a page fault,
> > and then it dereferences a bad pte in swap_vma_readahead(),
> >
> > 	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
> > 	     i++, pte++) {
> > 		pentry = *pte;   <— crashed here.
> > 		if (pte_none(pentry))
> 
> Is it possible to bisect this?
> 
> Because the crash point is identified, it may be helpful to collect and
> analyze the status of the faulting page table and readahead ptes.  But I
> am not familiar with the ARM64 architecture.  So I cannot help much
> here.

Ying, looks like the bug is still there today which manifests itself
into a different form. Looking at the logs, I believe it was involved
with swapoff(). Any other thought? I still have not found time to bisect
this yet.

[  785.477183][ T8727] BUG: KASAN: slab-out-of-bounds in swapin_readahead+0x7b8/0xbc0
swap_vma_readahead at mm/swap_state.c:759
(inlined by) swapin_readahead at mm/swap_state.c:803
[  785.484752][ T8727] Read of size 8 at addr ffff00886ecaffe8 by task trinity-c35/8727
[  785.492488][ T8727] 
[  785.494675][ T8727] CPU: 35 PID: 8727 Comm: trinity-c35 Not tainted 5.7.0-next-20200610 #3
[  785.502942][ T8727] Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS L50_5.13_1.11 06/18/2019
[  785.513387][ T8727] Call trace:
[  785.516538][ T8727]  dump_backtrace+0x0/0x398
[  785.520891][ T8727]  show_stack+0x14/0x20
[  785.524900][ T8727]  dump_stack+0x140/0x1b8
[  785.529087][ T8727]  print_address_description.isra.12+0x54/0x4a8
[  785.535185][ T8727]  kasan_report+0x134/0x1b8
[  785.539545][ T8727]  __asan_report_load8_noabort+0x2c/0x50
[  785.545036][ T8727]  swapin_readahead+0x7b8/0xbc0
[  785.549745][ T8727]  do_swap_page+0xb1c/0x19a0
[  785.554195][ T8727]  handle_mm_fault+0xf10/0x2b30
[  785.558905][ T8727]  do_page_fault+0x230/0x908
[  785.563354][ T8727]  do_translation_fault+0xe0/0x108
[  785.568323][ T8727]  do_mem_abort+0x64/0x180
[  785.572597][ T8727]  el1_sync_handler+0x188/0x1b8
[  785.577305][ T8727]  el1_sync+0x7c/0x100
[  785.581232][ T8727]  __arch_copy_to_user+0xc4/0x158
[  785.586115][ T8727]  __arm64_sys_sysinfo+0x2c/0xd0
[  785.590912][ T8727]  do_el0_svc+0x124/0x220
[  785.595100][ T8727]  el0_sync_handler+0x260/0x408
[  785.599807][ T8727]  el0_sync+0x140/0x180
[  785.603818][ T8727] 
[  785.606007][ T8727] Allocated by task 8673:
[  785.610193][ T8727]  save_stack+0x24/0x50
[  785.614208][ T8727]  __kasan_kmalloc.isra.13+0xc4/0xe0
[  785.619350][ T8727]  kasan_slab_alloc+0x14/0x20
[  785.623885][ T8727]  slab_post_alloc_hook+0x50/0xa8
[  785.628769][ T8727]  kmem_cache_alloc+0x18c/0x438
[  785.633479][ T8727]  create_object+0x58/0x960
[  785.637844][ T8727]  kmemleak_alloc+0x2c/0x38
[  785.642205][ T8727]  slab_post_alloc_hook+0x70/0xa8
[  785.647089][ T8727]  kmem_cache_alloc_trace+0x178/0x308
[  785.652322][ T8727]  refill_pi_state_cache.part.10+0x3c/0x1a8
[  785.658073][ T8727]  futex_lock_pi+0x404/0x5e0
[  785.662519][ T8727]  do_futex+0x790/0x1448
[  785.666618][ T8727]  __arm64_sys_futex+0x204/0x588
[  785.671411][ T8727]  do_el0_svc+0x124/0x220
[  785.675603][ T8727]  el0_sync_handler+0x260/0x408
[  785.680312][ T8727]  el0_sync+0x140/0x180
[  785.684322][ T8727] 
[  785.686510][ T8727] Freed by task 0:
[  785.690088][ T8727]  save_stack+0x24/0x50
[  785.694104][ T8727]  __kasan_slab_free+0x124/0x198
[  785.698899][ T8727]  kasan_slab_free+0x10/0x18
[  785.703340][ T8727]  slab_free_freelist_hook+0x110/0x298
[  785.708648][ T8727]  kmem_cache_free+0xc8/0x3e0
[  785.713175][ T8727]  free_object_rcu+0x1e0/0x3b8
[  785.717796][ T8727]  rcu_core+0x8bc/0xf40
[  785.721810][ T8727]  rcu_core_si+0xc/0x18
[  785.725825][ T8727]  efi_header_end+0x2d8/0x1204
[  785.730442][ T8727] 
[  785.732625][ T8727] The buggy address belongs to the object at ffff00886ecafd28
[  785.732625][ T8727]  which belongs to the cache kmemleak_object of size 368
[  785.746875][ T8727] The buggy address is located 336 bytes to the right of
[  785.746875][ T8727]  368-byte region [ffff00886ecafd28, ffff00886ecafe98)
[  785.760519][ T8727] The buggy address belongs to the page:
[  785.766009][ T8727] page:ffffffe021fbb280 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff00886ecaa8c8
[  785.776268][ T8727] flags: 0x7ffff800000200(slab)
[  785.780971][ T8727] raw: 007ffff800000200 ffffffe0222c12c8 ffffffe0223a1488 ffff000000323080
[  785.789410][ T8727] raw: ffff00886ecaa8c8 00000000005b001d 00000001ffffffff 0000000000000000
[  785.797849][ T8727] page dumped because: kasan: bad access85.811794][ T87270886ecaff00: fc  fc fc fc fc fc     ^
[  785.842727]  ffff00886ecb0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[  785.858703][ T8727] ==================================================================
[  785.866621][ T8727] Disabling lock debugging due to kernel taint
[  785.872714][ T8727] get_swap_device: Bad swap file entry 58025a5a5a5a5a5a
[  785.879523][ T8727] get_swap_device: Bad swap file entry 58025a5a5a5a5a5a
[  785.886322][ T8727] get_swap_device: Bad swap file entry 58025a5a5a5a5a5a