linux-kernel - [PATCH 5.16 272/285] KVM: avoid NULL pointer dereference in kvm_dirty_ring

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Date:   Tue, 12 Apr 2022 08:32:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Qiuhao Li <qiuhao@...ec.org>,
        Gaoning Pan <pgn@....edu.cn>, Yongkang Jia <kangel@....edu.cn>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.16 272/285] KVM: avoid NULL pointer dereference in kvm_dirty_ring_push

From: Paolo Bonzini <pbonzini@...hat.com>

commit 5593473a1e6c743764b08e3b6071cb43b5cfa6c4 upstream.

kvm_vcpu_release() will call kvm_dirty_ring_free(), freeing
ring->dirty_gfns and setting it to NULL.  Afterwards, it calls
kvm_arch_vcpu_destroy().

However, if closing the file descriptor races with KVM_RUN in such away
that vcpu->arch.st.preempted == 0, the following call stack leads to a
NULL pointer dereference in kvm_dirty_run_push():

 mark_page_dirty_in_slot+0x192/0x270 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3171
 kvm_steal_time_set_preempted arch/x86/kvm/x86.c:4600 [inline]
 kvm_arch_vcpu_put+0x34e/0x5b0 arch/x86/kvm/x86.c:4618
 vcpu_put+0x1b/0x70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:211
 vmx_free_vcpu+0xcb/0x130 arch/x86/kvm/vmx/vmx.c:6985
 kvm_arch_vcpu_destroy+0x76/0x290 arch/x86/kvm/x86.c:11219
 kvm_vcpu_destroy arch/x86/kvm/../../../virt/kvm/kvm_main.c:441 [inline]

The fix is to release the dirty page ring after kvm_arch_vcpu_destroy
has run.

Reported-by: Qiuhao Li <qiuhao@...ec.org>
Reported-by: Gaoning Pan <pgn@....edu.cn>
Reported-by: Yongkang Jia <kangel@....edu.cn>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 virt/kvm/kvm_main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -439,8 +439,8 @@ static void kvm_vcpu_init(struct kvm_vcp
 
 void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
 {
-	kvm_dirty_ring_free(&vcpu->dirty_ring);
 	kvm_arch_vcpu_destroy(vcpu);
+	kvm_dirty_ring_free(&vcpu->dirty_ring);
 
 	/*
 	 * No need for rcu_read_lock as VCPU_RUN is the only place that changes