4.9-stable review patch. If anyone has any objections, please let me know.
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From: Wanpeng Li kernellwp@gmail.com
commit bbeac2830f4de270bb48141681cb730aadf8dce1 upstream.
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 <pthread.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/wait.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/mman.h> #include <fcntl.h> #include <unistd.h> #include <linux/kvm.h> #include <stdio.h>
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 dvyukov@google.com Tested-by: Dmitry Vyukov dvyukov@google.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Dmitry Vyukov dvyukov@google.com Signed-off-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Cc: Zubin Mithra zsm@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/vmx.c | 1 + arch/x86/kvm/x86.c | 1 + 2 files changed, 2 insertions(+)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -5965,6 +5965,7 @@ static int handle_external_interrupt(str static int handle_triple_fault(struct kvm_vcpu *vcpu) { vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN; + vcpu->mmio_needed = 0; return 0; }
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6769,6 +6769,7 @@ static int vcpu_enter_guest(struct kvm_v } if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) { vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN; + vcpu->mmio_needed = 0; r = 0; goto out; }