On Tue, Oct 31 2023 at 22:36, syzbot wrote:
> general protection fault, probably for non-canonical address 0xdffffc003ffff113: 0000 [#1] PREEMPT SMP KASAN
> KASAN: probably user-memory-access in range [0x00000001ffff8898-0x00000001ffff889f]
> CPU: 1 PID: 5308 Comm: syz-executor.4 Not tainted 6.6.0-rc7-syzkaller-00142-g888cf78c29e2 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:lookup_object lib/debugobjects.c:195 [inline]
> RIP: 0010:lookup_object_or_alloc lib/debugobjects.c:564 [inline]
> RIP: 0010:__debug_object_init+0xf3/0x2b0 lib/debugobjects.c:634
> Code: d8 48 c1 e8 03 42 80 3c 20 00 0f 85 85 01 00 00 48 8b 1b 48 85 db 0f 84 9f 00 00 00 48 8d 7b 18 83 c5 01 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 0f 85 4c 01 00 00 4c 3b 73 18 75 c3 48 8d 7b 10 48
> RSP: 0018:ffffc900050e7d08 EFLAGS: 00010012
> RAX: 000000003ffff113 RBX: 00000001ffff8880 RCX: ffffffff8169123e
> RDX: 1ffffffff249b149 RSI: 0000000000000004 RDI: 00000001ffff8898
> RBP: 0000000000000003 R08: 0000000000000001 R09: 0000000000000216
> R10: 0000000000000003 R11: 0000000000000000 R12: dffffc0000000000
> R13: ffffffff924d8a48 R14: ffffc900050e7d90 R15: ffffffff924d8a50
> FS: 0000555556eec480(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa23ab065ee CR3: 000000007e5c1000 CR4: 0000000000350ee0
So this dies in debugobjects::lookup_object()
hlist_for_each_entry()
> 10: 48 8b 1b mov (%rbx),%rbx
Gets the next entry
> 13: 48 85 db test %rbx,%rbx
> 16: 0f 84 9f 00 00 00 je 0xbb
Checks for the termination condition (NULL pointer)
> 1c: 48 8d 7b 18 lea 0x18(%rbx),%rdi
Calculates the address of obj->object
> 20: 83 c5 01 add $0x1,%ebp
cnt++;
> 23: 48 89 f8 mov %rdi,%rax
> 26: 48 c1 e8 03 shr $0x3,%rax
KASAN shadow address calculation
> * 2a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction
Kasan accesses 0xdffffc003ffff113 and dies.
RBX contains the pointer to the next object: 0x00000001ffff8880 which is
clearly a user space address, but I have no idea where that might come
from. It's obviously data corruption of unknown provenience.
Unfortunately repro.syz does not hold up to its name and refuses to
reproduce.
Thanks,
tglx
On Wed, Nov 1, 2023 at 1:58 PM Thomas Gleixner <[email protected]> wrote:
>
> On Tue, Oct 31 2023 at 22:36, syzbot wrote:
> > general protection fault, probably for non-canonical address 0xdffffc003ffff113: 0000 [#1] PREEMPT SMP KASAN
> > KASAN: probably user-memory-access in range [0x00000001ffff8898-0x00000001ffff889f]
> > CPU: 1 PID: 5308 Comm: syz-executor.4 Not tainted 6.6.0-rc7-syzkaller-00142-g888cf78c29e2 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> > RIP: 0010:lookup_object lib/debugobjects.c:195 [inline]
> > RIP: 0010:lookup_object_or_alloc lib/debugobjects.c:564 [inline]
> > RIP: 0010:__debug_object_init+0xf3/0x2b0 lib/debugobjects.c:634
> > Code: d8 48 c1 e8 03 42 80 3c 20 00 0f 85 85 01 00 00 48 8b 1b 48 85 db 0f 84 9f 00 00 00 48 8d 7b 18 83 c5 01 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 0f 85 4c 01 00 00 4c 3b 73 18 75 c3 48 8d 7b 10 48
> > RSP: 0018:ffffc900050e7d08 EFLAGS: 00010012
> > RAX: 000000003ffff113 RBX: 00000001ffff8880 RCX: ffffffff8169123e
> > RDX: 1ffffffff249b149 RSI: 0000000000000004 RDI: 00000001ffff8898
> > RBP: 0000000000000003 R08: 0000000000000001 R09: 0000000000000216
> > R10: 0000000000000003 R11: 0000000000000000 R12: dffffc0000000000
> > R13: ffffffff924d8a48 R14: ffffc900050e7d90 R15: ffffffff924d8a50
> > FS: 0000555556eec480(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007fa23ab065ee CR3: 000000007e5c1000 CR4: 0000000000350ee0
>
> So this dies in debugobjects::lookup_object()
>
> hlist_for_each_entry()
>
> > 10: 48 8b 1b mov (%rbx),%rbx
>
> Gets the next entry
>
> > 13: 48 85 db test %rbx,%rbx
> > 16: 0f 84 9f 00 00 00 je 0xbb
>
> Checks for the termination condition (NULL pointer)
>
> > 1c: 48 8d 7b 18 lea 0x18(%rbx),%rdi
>
> Calculates the address of obj->object
>
> > 20: 83 c5 01 add $0x1,%ebp
>
> cnt++;
>
> > 23: 48 89 f8 mov %rdi,%rax
> > 26: 48 c1 e8 03 shr $0x3,%rax
>
> KASAN shadow address calculation
>
> > * 2a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction
>
> Kasan accesses 0xdffffc003ffff113 and dies.
>
> RBX contains the pointer to the next object: 0x00000001ffff8880 which is
> clearly a user space address, but I have no idea where that might come
> from. It's obviously data corruption of unknown provenience.
>
> Unfortunately repro.syz does not hold up to its name and refuses to
> reproduce.
For me, on a locally built kernel (gcc 13.2.0) it didn't work either.
But, interestingly, it does reproduce using the syzbot-built kernel
shared via the "Downloadable assets" [1] in the original report. The
repro crashed the kernel in ~1 minute.
[1] https://github.com/google/syzkaller/blob/master/docs/syzbot_assets.md
[ 125.919060][ C0] BUG: KASAN: stack-out-of-bounds in rb_next+0x10a/0x130
[ 125.921169][ C0] Read of size 8 at addr ffffc900048e7c60 by task
kworker/0:1/9
[ 125.923235][ C0]
[ 125.923243][ C0] CPU: 0 PID: 9 Comm: kworker/0:1 Not tainted
6.6.0-rc7-syzkaller-00142-g888cf78c29e2 #0
[ 125.924546][ C0] Hardware name: QEMU Standard PC (Q35 + ICH9,
2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 125.926915][ C0] Workqueue: events nsim_dev_trap_report_work
[ 125.929333][ C0]
[ 125.929341][ C0] Call Trace:
[ 125.929350][ C0] <IRQ>
[ 125.929356][ C0] dump_stack_lvl+0xd9/0x1b0
[ 125.931302][ C0] print_report+0xc4/0x620
[ 125.932115][ C0] ? __virt_addr_valid+0x5e/0x2d0
[ 125.933194][ C0] kasan_report+0xda/0x110
[ 125.934814][ C0] ? rb_next+0x10a/0x130
[ 125.936521][ C0] ? rb_next+0x10a/0x130
[ 125.936544][ C0] rb_next+0x10a/0x130
[ 125.936565][ C0] timerqueue_del+0xd4/0x140
[ 125.936590][ C0] __remove_hrtimer+0x99/0x290
[ 125.936613][ C0] __hrtimer_run_queues+0x55b/0xc10
[ 125.936638][ C0] ? enqueue_hrtimer+0x310/0x310
[ 125.936659][ C0] ? ktime_get_update_offsets_now+0x3bc/0x610
[ 125.936688][ C0] hrtimer_interrupt+0x31b/0x800
[ 125.936715][ C0] __sysvec_apic_timer_interrupt+0x105/0x3f0
[ 125.936737][ C0] sysvec_apic_timer_interrupt+0x8e/0xc0
[ 125.936755][ C0] </IRQ>
[ 125.936759][ C0] <TASK>
>
> Thanks,
>
> tglx
>
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