KASAN: out-of-bounds Write in nested_sync_vmcs12_to_shadow

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 9786cab6 Merge tag 'selinux-pr-20200416' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1110c920100000
kernel config: https://syzkaller.appspot.com/x/.config?x=5d351a1019ed81a2
dashboard link: https://syzkaller.appspot.com/bug?extid=6ad11779184a3afe9f7e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=141f46abe00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12b44c73e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=11b44c73e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=16b44c73e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6ad117...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: out-of-bounds in copy_vmcs12_to_enlightened arch/x86/kvm/vmx/nested.c:1820 [inline]
BUG: KASAN: out-of-bounds in nested_sync_vmcs12_to_shadow+0x49e3/0x4a60 arch/x86/kvm/vmx/nested.c:2000
Write of size 2 at addr ffffc90004db72e8 by task syz-executor.4/8294

CPU: 1 PID: 8294 Comm: syz-executor.4 Not tainted 5.7.0-rc1-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+0x188/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0x5/0x315 mm/kasan/report.c:382
__kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
kasan_report+0x33/0x50 mm/kasan/common.c:625
copy_vmcs12_to_enlightened arch/x86/kvm/vmx/nested.c:1820 [inline]
nested_sync_vmcs12_to_shadow+0x49e3/0x4a60 arch/x86/kvm/vmx/nested.c:2000
</IRQ>


Memory state around the buggy address:
ffffc90004db7180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc90004db7200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc90004db7280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ffffc90004db7300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc90004db7380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Paolo Bonzini]

On 21/04/20 02:15, syzbot wrote:
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+6ad117...@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: out-of-bounds in copy_vmcs12_to_enlightened arch/x86/kvm/vmx/nested.c:1820 [inline]
> BUG: KASAN: out-of-bounds in nested_sync_vmcs12_to_shadow+0x49e3/0x4a60 arch/x86/kvm/vmx/nested.c:2000
> Write of size 2 at addr ffffc90004db72e8 by task syz-executor.4/8294
>
> CPU: 1 PID: 8294 Comm: syz-executor.4 Not tainted 5.7.0-rc1-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+0x188/0x20d lib/dump_stack.c:118
> print_address_description.constprop.0.cold+0x5/0x315 mm/kasan/report.c:382
> __kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
> kasan_report+0x33/0x50 mm/kasan/common.c:625
> copy_vmcs12_to_enlightened arch/x86/kvm/vmx/nested.c:1820 [inline]
> nested_sync_vmcs12_to_shadow+0x49e3/0x4a60 arch/x86/kvm/vmx/nested.c:2000
> </IRQ>

That's a weird stack trace for a reproducer that is doing operations on
/dev/fb0. What's going on?

Paolo