[syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events

[syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    64980441d269 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=145b31d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=73696606574e3967
dashboard link: https://syzkaller.appspot.com/bug?extid=b1784a9a955885da51cd
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=110fcc0c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16340c0c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b721c3fbaf59/disk-64980441.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b28b1e530885/vmlinux-64980441.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5aee07cc8b41/bzImage-64980441.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b1784a9a955885da51cd@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5841 at arch/x86/kvm/lapic.c:3407 kvm_apic_accept_events+0x341/0x490 arch/x86/kvm/lapic.c:3407
Modules linked in:
CPU: 0 UID: 0 PID: 5841 Comm: syz-executor279 Not tainted 6.15.0-syzkaller-12058-g64980441d269 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:kvm_apic_accept_events+0x341/0x490 arch/x86/kvm/lapic.c:3407
Code: eb 0c e8 62 7b 72 00 eb 05 e8 5b 7b 72 00 45 31 ff 44 89 f8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 16 99 1a 0a cc e8 40 7b 72 00 90 <0f> 0b 90 e9 ec fd ff ff 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 4f
RSP: 0018:ffffc9000433f5c8 EFLAGS: 00010293
RAX: ffffffff814de090 RBX: 0000000000000002 RCX: ffff88802a735a00
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff81463863
R10: dffffc0000000000 R11: fffffbfff1f4201f R12: 0000000000000002
R13: dffffc0000000000 R14: ffff888030df4600 R15: ffff888031a682d8
FS:  0000555566bb6380(0000) GS:ffff888125c55000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002000 CR3: 0000000075360000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 vcpu_block arch/x86/kvm/x86.c:11298 [inline]
 vcpu_run+0x76f/0x6f70 arch/x86/kvm/x86.c:11335
 kvm_arch_vcpu_ioctl_run+0xfc9/0x1940 arch/x86/kvm/x86.c:11656
 kvm_vcpu_ioctl+0x95c/0xe90 virt/kvm/kvm_main.c:4461
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc83ec5e2f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff37b1fa98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fc83ec5e2f9
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
RBP: 0000200000bfe000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff37b1fac0
R13: 0000200000bff000 R14: 0000000000000004 R15: 0000000000000001
 </TASK>


---
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Re: [syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events

[Sean Christopherson]

On Thu, Jun 05, 2025, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    64980441d269 Merge tag 'bpf-fixes' of git://git.kernel.org..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=145b31d4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=73696606574e3967
> dashboard link: https://syzkaller.appspot.com/bug?extid=b1784a9a955885da51cd
> compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=110fcc0c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16340c0c580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/b721c3fbaf59/disk-64980441.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b28b1e530885/vmlinux-64980441.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/5aee07cc8b41/bzImage-64980441.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b1784a9a955885da51cd@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5841 at arch/x86/kvm/lapic.c:3407 kvm_apic_accept_events+0x341/0x490 arch/x86/kvm/lapic.c:3407
> Modules linked in:
> CPU: 0 UID: 0 PID: 5841 Comm: syz-executor279 Not tainted 6.15.0-syzkaller-12058-g64980441d269 #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:kvm_apic_accept_events+0x341/0x490 arch/x86/kvm/lapic.c:3407

Pretty straightforward; syzkaller sets MP_STATE to INIT_RECEIVED, and then
stuffs vmxon.  KVM, courtesy of commit 28bf28887976 ("KVM: x86: fix user
triggerable warning in kvm_apic_accept_events()"), only guards against the
opposite ordering.

Rather than play a losing game of whack-a-mole with ioctl ordering (SVM's GIF=0
case is even harder to deal with), I'm going to modify KVM to wait until KVM_RUN
to enforce the check, similar to how KVM handles the scenario where emulation is
required (due to !URG) but KVM can't emulate.

Re: [syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 0fe3e8d804fdcc09ef44fbffcad8c39261a03470
Author: Sean Christopherson <seanjc@google.com>
Date:   Thu Jun 5 19:50:17 2025 +0000

    KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1585c9e2580000
start commit:   64980441d269 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=26abb92f9ef9d1d0
dashboard link: https://syzkaller.appspot.com/bug?extid=b1784a9a955885da51cd
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12200c0c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16fd31d4580000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events

[Sean Christopherson]

On Sat, Oct 11, 2025, syzbot wrote:
> syzbot suspects this issue was fixed by commit:
> 
> commit 0fe3e8d804fdcc09ef44fbffcad8c39261a03470
> Author: Sean Christopherson <seanjc@google.com>
> Date:   Thu Jun 5 19:50:17 2025 +0000
> 
>     KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN

Doh, I used the wrong Reported-by in the changelog.

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1585c9e2580000
> start commit:   64980441d269 Merge tag 'bpf-fixes' of git://git.kernel.org..
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=26abb92f9ef9d1d0
> dashboard link: https://syzkaller.appspot.com/bug?extid=b1784a9a955885da51cd
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12200c0c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16fd31d4580000
> 
> If the result looks correct, please mark the issue as fixed by replying with:
> 
> #syz fix: KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

#syz fix: KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN