From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> Reported by syzkaller: *** Guest State *** CR0: actual=0x0000000080010031, shadow=0x0000000060000010, gh_mask=fffffffffffffff7 CR4: actual=0x0000000000002061, shadow=0x0000000000000000, gh_mask=ffffffffffffe8f1 CR3 = 0x000000002081e000 RSP = 0x000000000000fffa RIP = 0x0000000000000000 RFLAGS=0x00023000 DR7 = 0x0000000000000002 .......................... ------------[ cut here ]------------ WARNING: CPU: 6 PID: 24431 at /home/kernel/linux/arch/x86/kvm//x86.c:7302 kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] CPU: 6 PID: 24431 Comm: reprotest Tainted: G W OE 4.14.0+ #26 RIP: 0010:kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] RSP: 0018:ffff880291d179e0 EFLAGS: 00010202 Call Trace: ? synchronize_rcu.part.59+0x9b/0xf0 ? synchronize_rcu_expedited+0xa0/0xa0 ? kfree_call_rcu+0x20/0x20 ? trace_raw_output_rcu_utilization+0x70/0x70 ? kvm_arch_vcpu_runnable+0x220/0x220 [kvm] ? wait_for_completion+0x222/0x2a0 ? __wait_rcu_gp+0x1d3/0x230 ? kvm_vcpu_ioctl+0x479/0x880 [kvm] kvm_vcpu_ioctl+0x479/0x880 [kvm] ? kvm_dev_ioctl+0xba0/0xba0 [kvm] ? pick_next_task_fair+0x629/0xce0 ? sched_clock+0x1b/0x20 ? check_chain_key+0x131/0x1e0 ? lock_acquire+0x2c0/0x2c0 ? check_flags.part.44+0x62/0x250 ? check_chain_key+0x131/0x1e0 ? __lock_acquire+0xd2e/0x1cb0 do_vfs_ioctl+0x142/0x9a0 ? ioctl_preallocate+0x150/0x150 ? lock_acquire+0x2c0/0x2c0 ? lock_acquire+0x118/0x2c0 ? __lock_is_held+0x4b/0xe0 ? __fget+0x16a/0x250 SyS_ioctl+0x74/0x80 entry_SYSCALL_64_fastpath+0x23/0x9a The syzkaller testcase tries to setup the processor specific debug registers and configure vCPU for handling guest debug events through KVM_SET_GUEST_DEBUG. The KVM_SET_GUEST_DEBUG ioctl will get and set rflags in order to set TF bit if single step is needed. All regs' caches are reset to avail and GUEST_RFLAGS vmcs field is reset to 0x2 during vCPU reset. However, the cache of rflags is not reset during vCPU reset. The function vmx_get_rflags() returns an unreset rflags cache value since the cache is marked avail, it is 0 after boot. Vmentry fails if the rflags reserved bit 1 is 0. This patch fixes it by resetting both the GUEST_RFLAGS vmcs field and its cache to 0x2 during vCPU reset. Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> Cc: Nadav Amit <nadav.amit@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> --- arch/x86/kvm/vmx.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index b348920..131fa1c 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -5590,6 +5590,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) vmcs_write64(GUEST_IA32_DEBUGCTL, 0); } + vmx->rflags = 0x02; vmcs_writel(GUEST_RFLAGS, 0x02); kvm_rip_write(vcpu, 0xfff0); -- 2.7.4