KASAN: null-ptr-deref Read in init_emulate_ctxt

KASAN: null-ptr-deref Read in init_emulate_ctxt

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f5e94d10 Merge tag 'drm-next-2020-04-08' of git://anongit...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17e6d61be00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ca75979eeebf06c2
dashboard link: https://syzkaller.appspot.com/bug?extid=4a946e65aa25edfdb55f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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+4a946e65aa25edfdb55f@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in init_emulate_ctxt+0x497/0x4a0 arch/x86/kvm/x86.c:6424
Read of size 8 at addr 0000000000000005 by task syz-executor.2/9707

CPU: 1 PID: 9707 Comm: syz-executor.2 Not tainted 5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 __kasan_report.cold+0x5/0x4d mm/kasan/report.c:515
 kasan_report+0x33/0x50 mm/kasan/common.c:625
 init_emulate_ctxt+0x497/0x4a0 arch/x86/kvm/x86.c:6424
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 9707 Comm: syz-executor.2 Tainted: G    B             5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:221
 end_report+0x4d/0x53 mm/kasan/report.c:103
 __kasan_report.cold+0xd/0x4d mm/kasan/report.c:518
 kasan_report+0x33/0x50 mm/kasan/common.c:625
 init_emulate_ctxt+0x497/0x4a0 arch/x86/kvm/x86.c:6424
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..


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