linux-kernel - Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 7 Jul 2016 15:07:06 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Wanpeng Li <kernellwp@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Yunhong Jiang <yunhong.jiang@...el.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
Subject: Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit
 in nested guest

2016-07-07 15:02 GMT+08:00 Haozhong Zhang <haozhong.zhang@...el.com>:
> On 07/07/16 14:56, Wanpeng Li wrote:
>> 2016-07-07 14:48 GMT+08:00 Haozhong Zhang <haozhong.zhang@...el.com>:
>> > On 07/07/16 11:46, Wanpeng Li wrote:
>> >> From: Wanpeng Li <wanpeng.li@...mail.com>
>> >>
>> >> BUG: unable to handle kernel NULL pointer dereference at           (null)
>> >> IP: [<          (null)>]           (null)
>> >> PGD 0
>> >> Oops: 0010 [#1] SMP
>> >> Call Trace:
>> >>  ? kvm_lapic_expired_hv_timer+0x47/0x90 [kvm]
>> >>  handle_preemption_timer+0xe/0x20 [kvm_intel]
>> >>  vmx_handle_exit+0x169/0x15a0 [kvm_intel]
>> >>  ? kvm_arch_vcpu_ioctl_run+0xd5d/0x19d0 [kvm]
>> >>  kvm_arch_vcpu_ioctl_run+0xdee/0x19d0 [kvm]
>> >>  ? kvm_arch_vcpu_ioctl_run+0xd5d/0x19d0 [kvm]
>> >>  ? vcpu_load+0x1c/0x60 [kvm]
>> >>  ? kvm_arch_vcpu_load+0x57/0x260 [kvm]
>> >>  kvm_vcpu_ioctl+0x2d3/0x7c0 [kvm]
>> >>  do_vfs_ioctl+0x96/0x6a0
>> >>  ? __fget_light+0x2a/0x90
>> >>  SyS_ioctl+0x79/0x90
>> >>  do_syscall_64+0x68/0x180
>> >>  entry_SYSCALL64_slow_path+0x25/0x25
>> >> Code:  Bad RIP value.
>> >> RIP  [<          (null)>]           (null)
>> >>  RSP <ffff8800b5263c48>
>> >> CR2: 0000000000000000
>> >> ---[ end trace 9c70c48b1a2bc66e ]---
>> >>
>> >> This can be reproduced readily by preemption timer enabled on L0 and disabled
>> >> on L1.
>> >>
>> >> Preemption timer for nested VMX is emulated by hrtimer which is started on L2
>> >> entry, stopped on L2 exit and evaluated via the check_nested_events hook. However,
>> >> nested_vmx_exit_handled is always return true for preemption timer vmexit, then
>> >> the L1 preemption timer vmexit is captured and be treated as a L2 preemption
>> >> timer vmexit, incurr a nested vmexit dereference NULL pointer.
>> >>
>> >> This patch fix it by depending on check_nested_events to capture L2 preemption
>> >> timer(emulated hrtimer) expire and nested vmexit.
>> >>
>> >> Tested-by: Haozhong Zhang <haozhong.zhang@...el.com>
>> >> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> >> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> >> Cc: Yunhong Jiang <yunhong.jiang@...el.com>
>> >> Cc: Jan Kiszka <jan.kiszka@...mens.com>
>> >> Cc: Haozhong Zhang <haozhong.zhang@...el.com>
>> >> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> >> ---
>> >> v2 -> v3:
>> >>  * update patch subject
>> >> v1 -> v2:
>> >>  * fix typo in patch description
>> >>
>> >>  arch/x86/kvm/vmx.c | 2 ++
>> >>  1 file changed, 2 insertions(+)
>> >>
>> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> >> index 85e2f0a..29c16a8 100644
>> >> --- a/arch/x86/kvm/vmx.c
>> >> +++ b/arch/x86/kvm/vmx.c
>> >> @@ -8041,6 +8041,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
>> >>               return nested_cpu_has2(vmcs12, SECONDARY_EXEC_XSAVES);
>> >>       case EXIT_REASON_PCOMMIT:
>> >>               return nested_cpu_has2(vmcs12, SECONDARY_EXEC_PCOMMIT);
>> >> +     case EXIT_REASON_PREEMPTION_TIMER:
>> >> +             return false;
>> >
>> > If patch 2 can avoid accidentally enabling preemption timer in vmcs02,
>> > will this one still be needed?
>>
>> After complete "L1 TSC deadline timer to trigger while L2 is running",
>> L0's preemption timer fire when L2 is running can result in
>> (is_guest_mode(vcpu) && nested_vmx_exit_handled(vcpu)) be true, right?
>>
>
> In prepare_vmcs02():
>
>     exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
>     ...
>     vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, exec_control);
>
> so preemption timer will never be enabled while L2 guest is running.

It is not true after Paolo's patch.

Regards,
Wanpeng Li