Re: kvm: WARNING in kvm_arch_vcpu_ioctl_run

[Dmitry Vyukov]

-non-existent email address

On Wed, Aug 9, 2017 at 7:07 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Hello,
>
> syzkaller fuzzer has hit the following WARNING in kvm_arch_vcpu_ioctl_run.
> This is easily reproducible and reproducer is attached at the bottom.
> The report is on upstream commit
> 26c5cebfdb6ca799186f1e56be7d6f2480c5012c. This requires setting
> kvm-intel.unrestricted_guest=0 on the machine, with
> unrestricted_guest=1 the WARNING does not happen. Output of the
> program is:
>
> ret1=0 exit_reason=17 suberror=1
> ret2=0 exit_reason=8 suberror=65530
>
>
> WARNING: CPU: 1 PID: 2850 at arch/x86/kvm/x86.c:7223
> kvm_arch_vcpu_ioctl_run+0x213/0x5870 arch/x86/kvm/x86.c:7223
> CPU: 1 PID: 2850 Comm: a.out Not tainted 4.13.0-rc3+ #445
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:52
>  panic+0x1e4/0x417 kernel/panic.c:180
>  __warn+0x1c4/0x1d9 kernel/panic.c:541
>  report_bug+0x211/0x2d0 lib/bug.c:183
>  fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:190
>  do_trap_no_signal arch/x86/kernel/traps.c:224 [inline]
>  do_trap+0x260/0x390 arch/x86/kernel/traps.c:273
>  do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:310
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:323
>  invalid_op+0x1e/0x30 arch/x86/entry/entry_64.S:846
> RIP: 0010:kvm_arch_vcpu_ioctl_run+0x213/0x5870 arch/x86/kvm/x86.c:7222
> RSP: 0018:ffff8800627cf670 EFLAGS: 00010297
> RAX: ffff880066c44480 RBX: ffff88006b07f000 RCX: ffff880067d0845c
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff880067d08260
> RBP: ffff8800627cfa40 R08: 0000000000000001 R09: 0000000000000000
> R10: ffff8800627cfa58 R11: 0000000000000000 R12: 0000000000000001
> R13: 0000000000000000 R14: ffff88006b934880 R15: ffff880067d08040
>  kvm_vcpu_ioctl+0x64c/0x1010 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2592
>  vfs_ioctl fs/ioctl.c:45 [inline]
>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
>  SYSC_ioctl fs/ioctl.c:700 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>  entry_SYSCALL_64_fastpath+0x1f/0xbe
> RIP: 0033:0x44ccc9
> RSP: 002b:00007f9ecbc37db8 EFLAGS: 00000297 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000044ccc9
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
> RBP: 0000000000000082 R08: 00007f9ecbc38700 R09: 0000000000000000
> R10: 00007f9ecbc38700 R11: 0000000000000297 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007f9ecbc389c0 R15: 00007f9ecbc38700
>
>
>
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #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;
> }