linux-kernel - Re: kvm: WARNING in kvm_arch_vcpu_ioctl

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Date:   Wed, 9 Aug 2017 19:11:25 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        P J P <ppandit@...hat.com>,
        James Mattson <jmattson@...gle.com>,
        Haozhong Zhang <haozhong.zhang@...el.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Steve Rutherford <srutherford@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>
Subject: Re: kvm: WARNING in kvm_arch_vcpu_ioctl_run

On Wed, Aug 9, 2017 at 7:09 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> -non-existent email address
>
> On Wed, Aug 9, 2017 at 7:07 PM, Dmitry Vyukov <dvyukov@...gle.com> 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;
>> }



For the record, James suggested the following patch, but it does _not_ help:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c97c82814c4..21391c9241bc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5383,6 +5383,7 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu)
                vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
                vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
                vcpu->run->internal.ndata = 0;
+               vcpu->arch.pio.count = 0;
                r = EMULATE_FAIL;
        }
        kvm_queue_exception(vcpu, UD_VECTOR);