linux-kernel - Re: [syzbot] [kvm?] WARNING in kvm_gmem_fault_user

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Message-ID: <6989479f.050a0220.3b3015.0066.GAE@google.com>
Date: Sun, 08 Feb 2026 18:34:07 -0800
From: syzbot <syzbot+33a04338019ac7e43a44@...kaller.appspotmail.com>
To: kartikey406@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in __unmap_hugepage_range

Oops: general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
CPU: 0 UID: 0 PID: 6527 Comm: syz.4.21 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:hstate_inode include/linux/hugetlb.h:540 [inline]
RIP: 0010:hstate_file include/linux/hugetlb.h:756 [inline]
RIP: 0010:hstate_vma include/linux/hugetlb.h:772 [inline]
RIP: 0010:__unmap_hugepage_range+0x113/0x15f0 mm/hugetlb.c:5177
Code: 48 c1 ea 03 80 3c 02 00 0f 85 dd 12 00 00 48 8b 9b 38 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 cb 12 00 00 48 8b 43 50 48 89 44 24 10 48 05 a8
RSP: 0018:ffffc90003e9f700 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000200000800000
RDX: 000000000000000a RSI: ffffffff826be487 RDI: 0000000000000050
RBP: ffff88804f9ff000 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000400000 R11: 0000000000000000 R12: 0000000000000003
R13: ffff88804f9ff000 R14: 0000200000000000 R15: 0000200000800000
FS:  0000000000000000(0000) GS:ffff8881245d9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f37b2b31000 CR3: 000000006529d000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 unmap_single_vma+0x1ef/0x240 mm/memory.c:2058
 unmap_vmas+0x218/0x470 mm/memory.c:2104
 exit_mmap+0x181/0xae0 mm/mmap.c:1277
 __mmput+0x12a/0x410 kernel/fork.c:1173
 mmput+0x67/0x80 kernel/fork.c:1196
 exit_mm kernel/exit.c:581 [inline]
 do_exit+0x78a/0x2a30 kernel/exit.c:959
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1112
 get_signal+0x1ec7/0x21e0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x91/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x86/0x4b0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x4fe/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1b38f9aeb9
Code: Unable to access opcode bytes at 0x7f1b38f9ae8f.
RSP: 002b:00007f1b39d820e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007f1b39215fa8 RCX: 00007f1b38f9aeb9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f1b39215fac
RBP: 00007f1b39215fa0 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1b39216038 R14: 00007ffe5bb4b350 R15: 00007ffe5bb4b438
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:hstate_inode include/linux/hugetlb.h:540 [inline]
RIP: 0010:hstate_file include/linux/hugetlb.h:756 [inline]
RIP: 0010:hstate_vma include/linux/hugetlb.h:772 [inline]
RIP: 0010:__unmap_hugepage_range+0x113/0x15f0 mm/hugetlb.c:5177
Code: 48 c1 ea 03 80 3c 02 00 0f 85 dd 12 00 00 48 8b 9b 38 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 cb 12 00 00 48 8b 43 50 48 89 44 24 10 48 05 a8
RSP: 0018:ffffc90003e9f700 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000200000800000
RDX: 000000000000000a RSI: ffffffff826be487 RDI: 0000000000000050
RBP: ffff88804f9ff000 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000400000 R11: 0000000000000000 R12: 0000000000000003
R13: ffff88804f9ff000 R14: 0000200000000000 R15: 0000200000800000
FS:  0000000000000000(0000) GS:ffff8881246d9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6a9d71f286 CR3: 0000000060f0e000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	48 c1 ea 03          	shr    $0x3,%rdx
   4:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   8:	0f 85 dd 12 00 00    	jne    0x12eb
   e:	48 8b 9b 38 06 00 00 	mov    0x638(%rbx),%rbx
  15:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1c:	fc ff df
  1f:	48 8d 7b 50          	lea    0x50(%rbx),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 cb 12 00 00    	jne    0x12ff
  34:	48 8b 43 50          	mov    0x50(%rbx),%rax
  38:	48 89 44 24 10       	mov    %rax,0x10(%rsp)
  3d:	48                   	rex.W
  3e:	05                   	.byte 0x5
  3f:	a8                   	.byte 0xa8


Tested on:

commit:         05f7e89a Linux 6.19
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=125217fa580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=171d865a580000