Re: WARNING in __do_kernel_fault

From: Dmitry Vyukov <dvyukov@google.com>
To: syzbot <syzbot+45b6fce29ff97069e2c5@syzkaller.appspotmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Will Deacon <will@kernel.org>, Dave Martin <Dave.Martin@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: WARNING in __do_kernel_fault
Date: Wed, 27 Jan 2021 18:00:30 +0100	[thread overview]
Message-ID: <CACT4Y+agFz7Y32pkV7nObxB3KjCcN1p335h1HE4dr94rsDvndw@mail.gmail.com> (raw)
In-Reply-To: <0000000000009bbb7905b9e4a624@google.com>

On Wed, Jan 27, 2021 at 5:56 PM syzbot
<syzbot+45b6fce29ff97069e2c5@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    2ab38c17 mailmap: remove the "repo-abbrev" comment
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15a25264d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ad43be24faf1194c
> dashboard link: https://syzkaller.appspot.com/bug?extid=45b6fce29ff97069e2c5
> userspace arch: arm64
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+45b6fce29ff97069e2c5@syzkaller.appspotmail.com

This happens on arm64 instance with mte enabled.
There is a GPF in reiserfs_xattr_init on x86_64 reported:
https://syzkaller.appspot.com/bug?id=8abaedbdeb32c861dc5340544284167dd0e46cde
so I would assume it's just a plain NULL deref. Is this WARNING not
indicative of a kernel bug? Or there is something special about this
particular NULL deref?

> REISERFS (device loop0): Using rupasov hash to sort names
> ------------[ cut here ]------------
> Ignoring spurious kernel translation fault at virtual address 0000000000000030
> WARNING: CPU: 1 PID: 5380 at arch/arm64/mm/fault.c:364 __do_kernel_fault+0x198/0x1c0 arch/arm64/mm/fault.c:364
> Modules linked in:
> CPU: 1 PID: 5380 Comm: syz-executor.0 Not tainted 5.11.0-rc5-syzkaller-00037-g2ab38c17aac1 #0
> Hardware name: linux,dummy-virt (DT)
> pstate: 60400009 (nZCv daif +PAN -UAO -TCO BTYPE=--)
> pc : __do_kernel_fault+0x198/0x1c0 arch/arm64/mm/fault.c:364
> lr : __do_kernel_fault+0x198/0x1c0 arch/arm64/mm/fault.c:364
> sp : ffff800014933830
> x29: ffff800014933830 x28: f1ff00000c28bc00
> x27: ffff80001231db80 x26: f0ff00002054a0b8
> x25: 0000000000000000 x24: f1ff000004217680
> x23: 0000000097c78006 x22: 0000000000000030
> x21: 0000000000000025 x20: ffff800014933960
> x19: 0000000097c78006 x18: 00000000fffffffb
> x17: 0000000000000000 x16: 0000000000000000
> x15: 0000000000000020 x14: 6c656e72656b2073
> x13: 00000000000006f9 x12: ffff8000149334e0
> x11: ffff80001313b450 x10: 00000000ffffe000
> x9 : ffff80001313b450 x8 : ffff80001308b450
> x7 : ffff80001313b450 x6 : 0000000000000000
> x5 : ffff00007fbe1948 x4 : 0000000000015ff5
> x3 : 0000000000000001 x2 : 0000000000000000
> x1 : 0000000000000000 x0 : f1ff00000c28bc00
> Call trace:
>  __do_kernel_fault+0x198/0x1c0 arch/arm64/mm/fault.c:364
>  do_page_fault+0x1c0/0x3a0 arch/arm64/mm/fault.c:649
>  do_translation_fault+0xb4/0xc4 arch/arm64/mm/fault.c:660
>  do_mem_abort+0x44/0xbc arch/arm64/mm/fault.c:793
>  el1_abort+0x40/0x6c arch/arm64/kernel/entry-common.c:118
>  el1_sync_handler+0xb0/0xcc arch/arm64/kernel/entry-common.c:209
>  el1_sync+0x70/0x100 arch/arm64/kernel/entry.S:656
>  reiserfs_xattr_jcreate_nblocks fs/reiserfs/xattr.h:79 [inline]
>  reiserfs_security_init+0x98/0x10c fs/reiserfs/xattr_security.c:70
>  reiserfs_mkdir+0xf4/0x320 fs/reiserfs/namei.c:821
>  xattr_mkdir.constprop.0+0x24/0x3c fs/reiserfs/xattr.c:76
>  create_privroot fs/reiserfs/xattr.c:889 [inline]
>  reiserfs_xattr_init+0x16c/0x320 fs/reiserfs/xattr.c:1011
>  reiserfs_fill_super+0xa34/0xd20 fs/reiserfs/super.c:2177
>  mount_bdev+0x1c4/0x1f0 fs/super.c:1366
>  get_super_block+0x1c/0x30 fs/reiserfs/super.c:2606
>  legacy_get_tree+0x34/0x64 fs/fs_context.c:592
>  vfs_get_tree+0x2c/0xf0 fs/super.c:1496
>  do_new_mount fs/namespace.c:2881 [inline]
>  path_mount+0x3e8/0xaf0 fs/namespace.c:3211
>  do_mount fs/namespace.c:3224 [inline]
>  __do_sys_mount fs/namespace.c:3432 [inline]
>  __se_sys_mount fs/namespace.c:3409 [inline]
>  __arm64_sys_mount+0x1a8/0x2fc fs/namespace.c:3409
>  __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
>  invoke_syscall arch/arm64/kernel/syscall.c:49 [inline]
>  el0_svc_common.constprop.0+0x74/0x190 arch/arm64/kernel/syscall.c:159
>  do_el0_svc+0x78/0x90 arch/arm64/kernel/syscall.c:198
>  el0_svc+0x14/0x20 arch/arm64/kernel/entry-common.c:365
>  el0_sync_handler+0x1a8/0x1b0 arch/arm64/kernel/entry-common.c:381
>  el0_sync+0x190/0x1c0 arch/arm64/kernel/entry.S:699
>
>
> ---
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>
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