[PATCH v2] mm/kasan: Fix double free for kasan pXds

[Alexander Potapenko]

On Tue, Feb 24, 2026 at 2:23 PM Ritesh Harjani (IBM)
<ritesh.list at gmail.com> wrote:
>
> kasan_free_pxd() assumes the page table is always struct page aligned.
> But that's not always the case for all architectures. E.g. In case of
> powerpc with 64K pagesize, PUD table (of size 4096) comes from slab
> cache named pgtable-2^9. Hence instead of page_to_virt(pxd_page()) let's
> just directly pass the start of the pxd table which is passed as the 1st
> argument.
>
> This fixes the below double free kasan issue seen with PMEM:
>
> radix-mmu: Mapped 0x0000047d10000000-0x0000047f90000000 with 2.00 MiB pages
> ==================================================================
> BUG: KASAN: double-free in kasan_remove_zero_shadow+0x9c4/0xa20
> Free of addr c0000003c38e0000 by task ndctl/2164
>
> CPU: 34 UID: 0 PID: 2164 Comm: ndctl Not tainted 6.19.0-rc1-00048-gea1013c15392 #157 VOLUNTARY
> Hardware name: IBM,9080-HEX POWER10 (architected) 0x800200 0xf000006 of:IBM,FW1060.00 (NH1060_012) hv:phyp pSeries
> Call Trace:
>  dump_stack_lvl+0x88/0xc4 (unreliable)
>  print_report+0x214/0x63c
>  kasan_report_invalid_free+0xe4/0x110
>  check_slab_allocation+0x100/0x150
>  kmem_cache_free+0x128/0x6e0
>  kasan_remove_zero_shadow+0x9c4/0xa20
>  memunmap_pages+0x2b8/0x5c0
>  devm_action_release+0x54/0x70
>  release_nodes+0xc8/0x1a0
>  devres_release_all+0xe0/0x140
>  device_unbind_cleanup+0x30/0x120
>  device_release_driver_internal+0x3e4/0x450
>  unbind_store+0xfc/0x110
>  drv_attr_store+0x78/0xb0
>  sysfs_kf_write+0x114/0x140
>  kernfs_fop_write_iter+0x264/0x3f0
>  vfs_write+0x3bc/0x7d0
>  ksys_write+0xa4/0x190
>  system_call_exception+0x190/0x480
>  system_call_vectored_common+0x15c/0x2ec
> ---- interrupt: 3000 at 0x7fff93b3d3f4
> NIP:  00007fff93b3d3f4 LR: 00007fff93b3d3f4 CTR: 0000000000000000
> REGS: c0000003f1b07e80 TRAP: 3000   Not tainted  (6.19.0-rc1-00048-gea1013c15392)
> MSR:  800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 48888208  XER: 00000000
> <...>
> NIP [00007fff93b3d3f4] 0x7fff93b3d3f4
> LR [00007fff93b3d3f4] 0x7fff93b3d3f4
> ---- interrupt: 3000
>
>  The buggy address belongs to the object at c0000003c38e0000
>   which belongs to the cache pgtable-2^9 of size 4096
>  The buggy address is located 0 bytes inside of
>   4096-byte region [c0000003c38e0000, c0000003c38e1000)
>
>  The buggy address belongs to the physical page:
>  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3c38c
>  head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
>  memcg:c0000003bfd63e01
>  flags: 0x63ffff800000040(head|node=6|zone=0|lastcpupid=0x7ffff)
>  page_type: f5(slab)
>  raw: 063ffff800000040 c000000140058980 5deadbeef0000122 0000000000000000
>  raw: 0000000000000000 0000000080200020 00000000f5000000 c0000003bfd63e01
>  head: 063ffff800000040 c000000140058980 5deadbeef0000122 0000000000000000
>  head: 0000000000000000 0000000080200020 00000000f5000000 c0000003bfd63e01
>  head: 063ffff800000002 c00c000000f0e301 00000000ffffffff 00000000ffffffff
>  head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
>  page dumped because: kasan: bad access detected
>
> [  138.953636] [   T2164] Memory state around the buggy address:
> [  138.953643] [   T2164]  c0000003c38dff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  138.953652] [   T2164]  c0000003c38dff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  138.953661] [   T2164] >c0000003c38e0000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  138.953669] [   T2164]                    ^
> [  138.953675] [   T2164]  c0000003c38e0080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  138.953684] [   T2164]  c0000003c38e0100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  138.953692] [   T2164] ==================================================================
> [  138.953701] [   T2164] Disabling lock debugging due to kernel taint
>
> Fixes: 0207df4fa1a8 ("kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN")
> Cc: stable at vger.kernel.org
> Reported-by: Venkat Rao Bagalkote <venkat88 at linux.ibm.com>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list at gmail.com>
Reviewed-by: Alexander Potapenko <glider at google.com>