[PATCH v6 00/71] Introducing the Maple Tree

[Qian Cai]

On Tue, Feb 15, 2022 at 02:37:44PM +0000, Liam Howlett wrote:
> The maple tree is an RCU-safe range based B-tree designed to use modern
> processor cache efficiently.  There are a number of places in the kernel
> that a non-overlapping range-based tree would be beneficial, especially
> one with a simple interface.  The first user that is covered in this
> patch set is the vm_area_struct, where three data structures are
> replaced by the maple tree: the augmented rbtree, the vma cache, and the
> linked list of VMAs in the mm_struct.  The long term goal is to reduce
> or remove the mmap_sem contention.
> 
> The tree has a branching factor of 10 for non-leaf nodes and 16 for leaf
> nodes.  With the increased branching factor, it is significantly shorter than
> the rbtree so it has fewer cache misses.  The removal of the linked list
> between subsequent entries also reduces the cache misses and the need to pull
> in the previous and next VMA during many tree alterations.
> 
> This patch is based on v5.17-rc4
> 
> git: https://github.com/oracle/linux-uek/tree/howlett/maple/20220214

Just a heads-up. I noticed an use-after-free in today's linux-next below. I
am running out of time to fully triage this, but I noticed this is the only
series (not sure which revision) heavily touched mm/mmap.c recently there.

 BUG: KASAN: use-after-free in move_vma.isra.0
 Read of size 8 at addr ffff0009ce752ac8 by task systemd-logind/1280

 CPU: 21 PID: 1280 Comm: systemd-logind Not tainted 5.17.0-rc5-next-20220223-dirty #242
 Hardware name: MiTAC RAPTOR EV-883832-X3-0001/RAPTOR, BIOS 1.6 06/28/2020
 Call trace:
  dump_backtrace
  show_stack
  dump_stack_lvl
  print_address_description.constprop.0
  kasan_report
  __asan_report_load8_noabort
  move_vma.isra.0
  move_vma at /usr/src/linux-next/mm/mremap.c:714
  __do_sys_mremap
  __arm64_sys_mremap
  invoke_syscall
  el0_svc_common.constprop.0
  do_el0_svc
  el0_svc
  el0t_64_sync_handler
  el0t_64_sync

 Allocated by task 1280:
  kasan_save_stack
  __kasan_slab_alloc
  slab_post_alloc_hook
  kmem_cache_alloc
  vm_area_alloc
  vm_area_alloc at /usr/src/linux-next/kernel/fork.c:455
  mmap_region
  mmap_region at /usr/src/linux-next/mm/mmap.c:2585
  do_mmap
  vm_mmap_pgoff
  ksys_mmap_pgoff
  __arm64_sys_mmap
  invoke_syscall
  el0_svc_common.constprop.0
  do_el0_svc
  el0_svc
  el0t_64_sync_handler
  el0t_64_sync

 Freed by task 1280:
  kasan_save_stack
  kasan_set_track
  kasan_set_free_info
  __kasan_slab_free
  kmem_cache_free
  vm_area_free
  remove_vma
  remove_vma at /usr/src/linux-next/mm/mmap.c:187
  do_mas_align_munmap.isra.0
  remove_mt at /usr/src/linux-next/mm/mmap.c:2176
  (inlined by) do_mas_align_munmap at /usr/src/linux-next/mm/mmap.c:2437
  do_mas_munmap
  do_mas_munmap at /usr/src/linux-next/mm/mmap.c:2483
  do_munmap
  move_vma.isra.0
  __do_sys_mremap
  __arm64_sys_mremap
  invoke_syscall
  el0_svc_common.constprop.0
  do_el0_svc
  el0_svc
  el0t_64_sync_handler
  el0t_64_sync

 The buggy address belongs to the object at ffff0009ce752aa8
  which belongs to the cache vm_area_struct of size 144
 The buggy address is located 32 bytes inside of
  144-byte region [ffff0009ce752aa8, ffff0009ce752b38)
 The buggy address belongs to the page:
 page:fffffc002739d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xa4e750
 head:fffffc002739d400 order:2 compound_mapcount:0 compound_pincount:0
 memcg:ffff0009ce456e01
 flags: 0xbfffc0000010200(slab|head|node=0|zone=2|lastcpupid=0xffff)
 raw: 0bfffc0000010200 fffffc002739f108 fffffc00273a3b08 ffff000800f53380
 raw: 0000000000000000 0000000000210021 00000001ffffffff ffff0009ce456e01
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff0009ce752980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff0009ce752a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 >ffff0009ce752a80: fc fc fc fc fc fa fb fb fb fb fb fb fb fb fb fb
                                               ^
  ffff0009ce752b00: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc
  ffff0009ce752b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc