KASAN: null-ptr-deref Write in kvm_vcpu_halt

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17d9bfa9100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=be4578b3f1083656
dashboard link: https://syzkaller.appspot.com/bug?extid=76004d8cdf5443dcd8e7
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+76004d8cdf5443dcd8e7@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: null-ptr-deref in kvm_vcpu_halt+0xea/0x110 arch/x86/kvm/x86.c:7546
Write of size 4 at addr 0000000000000000 by task syz-executor.0/11111

CPU: 1 PID: 11111 Comm: syz-executor.0 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 __kasan_report mm/kasan/report.c:517 [inline]
 kasan_report+0x151/0x1d0 mm/kasan/report.c:530
 kvm_vcpu_halt+0xea/0x110 arch/x86/kvm/x86.c:7546
 </IRQ>
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 11111 Comm: syz-executor.0 Tainted: G    B             5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 panic+0x264/0x7a0 kernel/panic.c:221
 end_report mm/kasan/report.c:104 [inline]
 __kasan_report mm/kasan/report.c:520 [inline]
 kasan_report+0x1c9/0x1d0 mm/kasan/report.c:530
 kvm_vcpu_halt+0xea/0x110 arch/x86/kvm/x86.c:7546
 </IRQ>
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..


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