linux-kernel - [PATCH tip] KVM: nSVM: avoid freeing uninitialized pointers in svm_set_nested

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Date:   Mon, 14 Sep 2020 15:37:25 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     x86@...nel.org
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Colin King <colin.king@...onical.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH tip] KVM: nSVM: avoid freeing uninitialized pointers in svm_set_nested_state()

The save and ctl pointers are passed uninitialized to kfree() when
svm_set_nested_state() follows the 'goto out_set_gif' path. While
the issue could've been fixed by initializing these on-stack varialbles
to NULL, it seems preferable to eliminate 'out_set_gif' label completely
as it is not actually a failure path and duplicating a single svm_set_gif()
call doesn't look too bad.

Fixes: 6ccbd29ade0d ("KVM: SVM: nested: Don't allocate VMCB structures on stack")
Addresses-Coverity: ("Uninitialized pointer read")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Reported-by: Joerg Roedel <jroedel@...e.de>
Reported-by: Colin King <colin.king@...onical.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/svm/nested.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 598a769f1961..67e6d053985d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1094,7 +1094,8 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	if (!(kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE)) {
 		svm_leave_nested(svm);
-		goto out_set_gif;
+		svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
+		return 0;
 	}
 
 	if (!page_address_valid(vcpu, kvm_state->hdr.svm.vmcb_pa))
@@ -1150,7 +1151,6 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	if (!nested_svm_vmrun_msrpm(svm))
 		return -EINVAL;
 
-out_set_gif:
 	svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
 
 	ret = 0;
-- 
2.25.4