linux-kernel - Re: [PATCH v4 4/4] mm/page_table_check: check entries at pmd levels

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Date:   Wed, 26 Jan 2022 11:26:09 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, pjt@...gle.com, weixugc@...gle.com,
        gthelen@...gle.com, mingo@...hat.com, will@...nel.org,
        rppt@...nel.org, dave.hansen@...ux.intel.com, hpa@...or.com,
        aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com, hughd@...gle.com,
        ziy@...dia.com, anshuman.khandual@....com
Subject: Re: [PATCH v4 4/4] mm/page_table_check: check entries at pmd
 levels

On Wed, 26 Jan 2022, Pasha Tatashin wrote:

> syzbot detected a case where the page table counters were not properly
> updated.
> 
> syzkaller login:  ------------[ cut here ]------------
> kernel BUG at mm/page_table_check.c:162!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 3099 Comm: pasha Not tainted 5.16.0+ #48
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO4
> RIP: 0010:__page_table_check_zero+0x159/0x1a0
> Code: 7d 3a b2 ff 45 39 f5 74 2a e8 43 38 b2 ff 4d 85 e4 01
> RSP: 0018:ffff888010667418 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000
> RDX: ffff88800cea8680 RSI: ffffffff81becaf9 RDI: 0000000003
> RBP: ffff888010667450 R08: 0000000000000001 R09: 0000000000
> R10: ffffffff81becaab R11: 0000000000000001 R12: ffff888008
> R13: 0000000000000001 R14: 0000000000000200 R15: dffffc0000
> FS:  0000000000000000(0000) GS:ffff888035e00000(0000) knlG0
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffd875cad00 CR3: 00000000094ce000 CR4: 0000000000
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000
> Call Trace:
>  <TASK>
>  free_pcp_prepare+0x3be/0xaa0
>  free_unref_page+0x1c/0x650
>  ? trace_hardirqs_on+0x6a/0x1d0
>  free_compound_page+0xec/0x130
>  free_transhuge_page+0x1be/0x260
>  __put_compound_page+0x90/0xd0
>  release_pages+0x54c/0x1060
>  ? filemap_remove_folio+0x161/0x210
>  ? lock_downgrade+0x720/0x720
>  ? __put_page+0x150/0x150
>  ? filemap_free_folio+0x164/0x350
>  __pagevec_release+0x7c/0x110
>  shmem_undo_range+0x85e/0x1250
> ...
> 
> The repro involved having a huge page that is split due to uprobe event
> temporarily replacing one of the pages in the huge page. Later the huge
> page was combined again, but the counters were off, as the PTE level
> was not properly updated.
> 
> Make sure that when PMD is cleared and prior to freeing the level the
> PTEs are updated.
> 
> Fixes: df4e817b7108 ("mm: page table check")
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>

Acked-by: David Rientjes <rientjes@...gle.com>