Re: general protection fault in hrtimer_active (2)

[Paolo Bonzini]

On 27/02/2018 13:19, Dmitry Vyukov wrote:
> On Tue, Feb 27, 2018 at 1:18 PM, syzbot
> <syzbot+fb7a33a4b6c35007a72b@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzbot hit the following crash on upstream commit
>> 6f70eb2b00eb416146247c65003d31f4df983ce0 (Mon Feb 26 21:22:45 2018 +0000)
>> Merge branch 'idr-2018-02-06' of
>> git://git.infradead.org/users/willy/linux-dax
>>
>> So far this crash happened 867 times on upstream.
>> Unfortunately, I don't have any reproducer for this crash yet.
>> Raw console output is attached.
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached.
> 
> 
> Paulo,
> 
> This started happening on syzbot with threatening frequency, and it
> looks like it may be related to your recent "KVM: x86: move LAPIC
> initialization after VMCS creation".

Yeah, that's the typical thing that will never happen in real-world
testcases but very much for syzkaller.

This will fix it.

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 924ac8ce9d50..b1c50b78876b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2002,14 +2002,12 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu,
u64 value)

 void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
-	struct kvm_lapic *apic;
+	struct kvm_lapic *apic = vcpu->arch.apic;
 	int i;

 	apic_debug("%s\n", __func__);
-
-	ASSERT(vcpu);
-	apic = vcpu->arch.apic;
-	ASSERT(apic != NULL);
+	if (!apic)
+		return;

 	/* Stop the timer in case it's a reset to an active apic */
 	hrtimer_cancel(&apic->lapic_timer.timer);


Paolo

> 
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+fb7a33a4b6c35007a72b@xxxxxxxxxxxxxxxxxxxxxxxxx
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>> 8021q: adding VLAN 0 to HW filter on device bond0
>> IPv6: ADDRCONF(NETDEV_UP): bond0: link is not ready
>> 8021q: adding VLAN 0 to HW filter on device bond0
>> kasan: CONFIG_KASAN_INLINE enabled
>> kasan: GPF could be caused by NULL-ptr deref or user memory access
>> general protection fault: 0000 [#1] SMP KASAN
>> Dumping ftrace buffer:
>>    (ftrace buffer empty)
>> Modules linked in:
>> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
>> CPU: 1 PID: 5486 Comm: syz-executor1 Not tainted 4.16.0-rc3+ #331
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> RIP: 0010:__read_once_size include/linux/compiler.h:188 [inline]
>> RIP: 0010:hrtimer_active+0x1da/0x3c0 kernel/time/hrtimer.c:1277
>> RSP: 0018:ffff8801b4ebf3c0 EFLAGS: 00010202
>> RAX: 0000000000000008 RBX: 1ffff100369d7ea5 RCX: ffffffff81610225
>> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
>> RDX: 0000000000010000 RSI: ffffc90001e1b000 RDI: 0000000000000010
>> RBP: ffff8801b4ebf500 R08: 0000000000002c02 R09: 0000000000000000
>> R10: 0000000000000011 R11: ffffed00365cb078 R12: 0000000000000010
>> R13: 0000000000000000 R14: ffffed00369d7e83 R15: dffffc0000000000
>> FS:  00007f8f8c80b700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f8f8c7ea000 CR3: 00000001b4577003 CR4: 00000000001626e0
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>>  hrtimer_try_to_cancel+0x91/0x5b0 kernel/time/hrtimer.c:1128
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>>  hrtimer_cancel+0x22/0x40 kernel/time/hrtimer.c:1154
>>  kvm_lapic_reset+0x93/0xf40 arch/x86/kvm/lapic.c:2015
>>  kvm_arch_vcpu_setup+0x31/0x50 arch/x86/kvm/x86.c:7978
>>  kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:2459
>> [inline]
>>  kvm_vm_ioctl+0x52d/0x1cf0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2949
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
>> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>>  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>> IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
>>  entry_SYSCALL_64_after_hwframe+0x42/0xb7
>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> RIP: 0033:0x453d69
>> RSP: 002b:00007f8f8c80ac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 00007f8f8c80b6d4 RCX: 0000000000453d69
>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000014
>> RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
>> R13: 000000000000020e R14: 00000000006f31f0 R15: 0000000000000000
>> Code:
>> kasan: CONFIG_KASAN_INLINE enabled
>> ff ff 48 8d 85 18 ff ff ff 48 c1
>> kasan: GPF could be caused by NULL-ptr deref or user memory access
>> e8 03 4e 8d 34 38 e8 1b f2 0f 00 48 8b 85 f0 fe ff ff c6 00 00 48 8b 85 d8
>> fe ff ff 48 c1 e8 03 <42> 80 3c 38 00 0f 85 c2 01 00 00 48 8b 85 e8 fe ff ff
>> 48 8b 58
>> RIP: __read_once_size include/linux/compiler.h:188 [inline] RSP:
>> ffff8801b4ebf3c0
>> RIP: hrtimer_active+0x1da/0x3c0 kernel/time/hrtimer.c:1277 RSP:
>> ffff8801b4ebf3c0
>> general protection fault: 0000 [#2] SMP KASAN
>> ---[ end trace a73097188f35aad4 ]---
>> Dumping ftrace buffer:
>>    (ftrace buffer empty)
>> Modules linked in:
>>
>>
>> ---
>> This bug is generated by a dumb bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for details.
>> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
>>
>> syzbot will keep track of this bug report.
>> If you forgot to add the Reported-by tag, once the fix for this bug is
>> merged
>> into any tree, please reply to this email with:
>> #syz fix: exact-commit-title
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