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* [syzbot] [virt?] BUG: unable to handle kernel paging request in __run_timers (3)
@ 2026-11-12  5:56 syzbot
  2026-11-12 12:41 ` Pimyn Girgis
  0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2026-11-12  5:56 UTC (permalink / raw)
  To: ajay.kaher, alexey.makhalov, bcm-kernel-feedback-list, bp,
	dave.hansen, hpa, jgross, linux-kernel, mingo, syzkaller-bugs,
	tglx, virtualization, x86

Hello,

syzbot found the following issue on:

HEAD commit:    d164c7d754f0 Merge tag 'devicetree-fixes-for-7.4-1' of git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=179566fd580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1cf189394a856f11
dashboard link: https://syzkaller.appspot.com/bug?extid=0d91f453e89c72a04157
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=173a724e580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d164c7d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0f548ae8bf9e/vmlinux-d164c7d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/79563ef77b97/bzImage-d164c7d7.xz

AI-generated root cause summary:
proc_bus_pci_write() in drivers/pci/proc.c allows userspace to write raw values
directly into the PCI configuration space of PCI devices without restricting
writes to critical platform host bridge registers when lockdown is not active.
Writing to device 00:00.0 (the Q35 Host Bridge / DRAM Controller) overwrites
memory controller registers, causing QEMU to unmap system RAM and return
all-ones (0xffffffffffffffff) for affected physical addresses. Consequently,
when the timer subsystem in __run_timers() dequeues an active timer from an
affected page, entry->next and entry->pprev evaluate to 0xffffffffffffffff,
causing __hlist_del() to trigger a fatal supervisor write page fault at address
0xffffffffffffffff.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=0d91f453e89c72a04157

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0d91f453e89c72a04157@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: ffffffffffffffff
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD fd99067 P4D fd99067 PUD fd9b067 PMD 0 
Oops: Oops: 0002 [#1] SMP KASAN NOPTI
CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__hlist_del include/linux/list.h:1045 [inline]
RIP: 0010:detach_timer kernel/time/timer.c:892 [inline]
RIP: 0010:expire_timers kernel/time/timer.c:1783 [inline]
RIP: 0010:__run_timers+0x68a/0xb00 kernel/time/timer.c:2375
Code: 8b 3b 48 89 f8 48 c1 e8 03 42 80 3c 20 00 0f 85 08 03 00 00 48 8b 43 08 48 89 c2 48 c1 ea 03 42 80 3c 22 00 0f 85 db 02 00 00 <4c> 89 38 48 89 44 24 08 4d 85 ff 74 24 e8 54 50 15 00 49 8d 7f 08
RSP: 0018:ffffc90000658d48 EFLAGS: 00010046
RAX: ffffffffffffffff RBX: ffff8880456d98d8 RCX: 0000000000000102
RDX: 1fffffffffffffff RSI: ffffffff81f92b99 RDI: ffff8880456d98e0
RBP: ffffc90000658e08 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff926ab25f R11: 0000000000000001 R12: dffffc0000000000
R13: fffff520000cb1c1 R14: ffff88806a2266c0 R15: ffffffffffffffff
FS:  0000000000000000(0000) GS:ffff8880d4675000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffff CR3: 0000000059bd9000 CR4: 0000000000352ef0
Call Trace:
 <IRQ>
 __run_timer_base kernel/time/timer.c:2387 [inline]
 __run_timer_base kernel/time/timer.c:2379 [inline]
 run_timer_base+0x114/0x190 kernel/time/timer.c:2396
 run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2406
 handle_softirqs+0x216/0xa20 kernel/softirq.c:669
 __do_softirq kernel/softirq.c:703 [inline]
 invoke_softirq kernel/softirq.c:542 [inline]
 __irq_exit_rcu+0x178/0x220 kernel/softirq.c:786
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:809
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: 67 a0 02 e9 43 61 03 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d c3 6d 1c 00 fb f4 <c3> cc cc cc cc 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000197e00 EFLAGS: 00000206
RAX: 000000000004ea47 RBX: ffff888020aba580 RCX: ffffffff8bef5325
RDX: 0000000000000001 RSI: ffffffff8e629989 RDI: ffffffff8c835980
RBP: ffffed10041574b0 R08: 0000000000000001 R09: ffffed100d446825
R10: ffff88806a23412b R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 1ffff92000032fc4 R15: dffffc0000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
 default_idle+0x9/0x10 arch/x86/kernel/process.c:768
 default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x3ae/0x5b0 kernel/sched/idle.c:355
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:458
 start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x158
 </TASK>
Modules linked in:
CR2: ffffffffffffffff
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	8b 3b                	mov    (%rbx),%edi
   2:	48 89 f8             	mov    %rdi,%rax
   5:	48 c1 e8 03          	shr    $0x3,%rax
   9:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1)
   e:	0f 85 08 03 00 00    	jne    0x31c
  14:	48 8b 43 08          	mov    0x8(%rbx),%rax
  18:	48 89 c2             	mov    %rax,%rdx
  1b:	48 c1 ea 03          	shr    $0x3,%rdx
  1f:	42 80 3c 22 00       	cmpb   $0x0,(%rdx,%r12,1)
  24:	0f 85 db 02 00 00    	jne    0x305
* 2a:	4c 89 38             	mov    %r15,(%rax) <-- trapping instruction
  2d:	48 89 44 24 08       	mov    %rax,0x8(%rsp)
  32:	4d 85 ff             	test   %r15,%r15
  35:	74 24                	je     0x5b
  37:	e8 54 50 15 00       	call   0x155090
  3c:	49 8d 7f 08          	lea    0x8(%r15),%rdi


---
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^ permalink raw reply	[flat|nested] 2+ messages in thread
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2026-11-12  5:56 [syzbot] [virt?] BUG: unable to handle kernel paging request in __run_timers (3) syzbot
2026-11-12 12:41 ` Pimyn Girgis

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