From: Wanpeng Li Date: Thu, 10 Aug 2017 05:33:12 +0000 (-0700) Subject: KVM: X86: Fix residual mmio emulation request to userspace X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=bbeac2830f4de270bb48141681cb730aadf8dce1;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git KVM: X86: Fix residual mmio emulation request to userspace Reported by syzkaller: The kvm-intel.unrestricted_guest=0 WARNING: CPU: 5 PID: 1014 at /home/kernel/data/kvm/arch/x86/kvm//x86.c:7227 kvm_arch_vcpu_ioctl_run+0x38b/0x1be0 [kvm] CPU: 5 PID: 1014 Comm: warn_test Tainted: G W OE 4.13.0-rc3+ #8 RIP: 0010:kvm_arch_vcpu_ioctl_run+0x38b/0x1be0 [kvm] Call Trace: ? put_pid+0x3a/0x50 ? rcu_read_lock_sched_held+0x79/0x80 ? kmem_cache_free+0x2f2/0x350 kvm_vcpu_ioctl+0x340/0x700 [kvm] ? kvm_vcpu_ioctl+0x340/0x700 [kvm] ? __fget+0xfc/0x210 do_vfs_ioctl+0xa4/0x6a0 ? __fget+0x11d/0x210 SyS_ioctl+0x79/0x90 entry_SYSCALL_64_fastpath+0x23/0xc2 ? __this_cpu_preempt_check+0x13/0x20 The syszkaller folks reported a residual mmio emulation request to userspace due to vm86 fails to emulate inject real mode interrupt(fails to read CS) and incurs a triple fault. The vCPU returns to userspace with vcpu->mmio_needed == true and KVM_EXIT_SHUTDOWN exit reason. However, the syszkaller testcase constructs several threads to launch the same vCPU, the thread which lauch this vCPU after the thread whichs get the vcpu->mmio_needed == true and KVM_EXIT_SHUTDOWN will trigger the warning. #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include #include #include #include int kvmcpu; struct kvm_run *run; void* thr(void* arg) { int res; res = ioctl(kvmcpu, KVM_RUN, 0); printf("ret1=%d exit_reason=%d suberror=%d\n", res, run->exit_reason, run->internal.suberror); return 0; } void test() { int i, kvm, kvmvm; pthread_t th[4]; kvm = open("/dev/kvm", O_RDWR); kvmvm = ioctl(kvm, KVM_CREATE_VM, 0); kvmcpu = ioctl(kvmvm, KVM_CREATE_VCPU, 0); run = (struct kvm_run*)mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, kvmcpu, 0); srand(getpid()); for (i = 0; i < 4; i++) { pthread_create(&th[i], 0, thr, 0); usleep(rand() % 10000); } for (i = 0; i < 4; i++) pthread_join(th[i], 0); } int main() { for (;;) { int pid = fork(); if (pid < 0) exit(1); if (pid == 0) { test(); exit(0); } int status; while (waitpid(pid, &status, __WALL) != pid) {} } return 0; } This patch fixes it by resetting the vcpu->mmio_needed once we receive the triple fault to avoid the residue. Reported-by: Dmitry Vyukov Tested-by: Dmitry Vyukov Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Dmitry Vyukov Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 46d08b389e36..c7cf5b11994a 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -5862,6 +5862,7 @@ static int handle_external_interrupt(struct kvm_vcpu *vcpu) static int handle_triple_fault(struct kvm_vcpu *vcpu) { vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN; + vcpu->mmio_needed = 0; return 0; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 69b72c9e1f12..e40a779711a9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6771,6 +6771,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) { vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN; + vcpu->mmio_needed = 0; r = 0; goto out; }