[syzbot] [kvm?] KMSAN: uninit-value in em_ret

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b401b621758e Linux 6.8-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15cd41c2180000
kernel config: https://syzkaller.appspot.com/x/.config?x=1b015d567058472
dashboard link: https://syzkaller.appspot.com/bug?extid=ee5eb98a07d2c1fb30df
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c32ff3cbe7ed/disk-b401b621.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/17621a870a21/vmlinux-b401b621.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b06ad3ca55ee/bzImage-b401b621.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ee5eb9...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in assign_eip_near arch/x86/kvm/emulate.c:829 [inline]
BUG: KMSAN: uninit-value in em_ret+0x124/0x130 arch/x86/kvm/emulate.c:2238
assign_eip_near arch/x86/kvm/emulate.c:829 [inline]
em_ret+0x124/0x130 arch/x86/kvm/emulate.c:2238
x86_emulate_insn+0x1d87/0x5880 arch/x86/kvm/emulate.c:5292
x86_emulate_instruction+0x13c9/0x30a0 arch/x86/kvm/x86.c:9171
kvm_emulate_instruction arch/x86/kvm/x86.c:9251 [inline]
complete_emulated_io arch/x86/kvm/x86.c:11208 [inline]
complete_emulated_mmio+0x70b/0x8b0 arch/x86/kvm/x86.c:11268
kvm_arch_vcpu_ioctl_run+0x1837/0xb890 arch/x86/kvm/x86.c:11380
kvm_vcpu_ioctl+0xbfc/0x1770 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4441
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0x225/0x410 fs/ioctl.c:857
__x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Local variable eip created at:
em_ret+0x37/0x130 arch/x86/kvm/emulate.c:2234
x86_emulate_insn+0x1d87/0x5880 arch/x86/kvm/emulate.c:5292

CPU: 0 PID: 5793 Comm: syz-executor.0 Not tainted 6.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Sean Christopherson]

#syz fix: KVM: x86: Clean up partially uninitialized integer in emulate_pop()