linux-kernel - [PATCH v2] KVM: nVMX: Fix preemption timer kernel NULL pointer dereference

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Date:	Wed,  6 Jul 2016 18:29:58 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	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>,
	Haozhong Zhang <haozhong.zhang@...el.com>
Subject: [PATCH v2] KVM: nVMX: Fix preemption timer kernel NULL pointer dereference

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.

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>
---
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;
 	default:
 		return true;
 	}
-- 
1.9.1