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Date:   Mon, 14 Jan 2019 15:47:28 -0800
In-Reply-To: <6f79d9be-fa76-3a06-2612-f44f3a18ece7@redhat.com>
Message-Id: <20190114234728.49239-1-tmroeder@google.com>
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Subject: [RFC PATCH] kvm: x86/vmx: Use kzalloc for cached_vmcs12
From:   Tom Roeder <tmroeder@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>,
        "=?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?=" <rkrcmar@redhat.com>
Cc:     Liran Alon <liran.alon@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Tom Roeder <tmroeder@google.com>,
        syzbot+ded1696f6b50b615b630@syzkaller.appspotmail.com
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Sender: linux-kernel-owner@vger.kernel.org
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This changes the allocation of cached_vmcs12 to use kzalloc instead of
kmalloc. This removes the information leak found by Syzkaller (see
Reported-by) in this case and prevents similar leaks from happening
based on cached_vmcs12.

The email from Syszkaller led to a discussion about a patch in early
November on the KVM list (I've made this a reply to that thread), but
the current upstream kernel still has kmalloc instead of kzalloc for
cached_vmcs12 and cached_shadow_vmcs12. This RFC proposes changing to
kzalloc for defense in depth.

Tested: rebuilt but not tested, since this is an RFC

Reported-by: syzbot+ded1696f6b50b615b630@syzkaller.appspotmail.com
Signed-off-by: Tom Roeder <tmroeder@google.com>
---
 arch/x86/kvm/vmx/nested.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 2616bd2c7f2c7..ad46667042c7a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4140,11 +4140,11 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
 	if (r < 0)
 		goto out_vmcs02;
 
-	vmx->nested.cached_vmcs12 = kmalloc(VMCS12_SIZE, GFP_KERNEL);
+	vmx->nested.cached_vmcs12 = kzalloc(VMCS12_SIZE, GFP_KERNEL);
 	if (!vmx->nested.cached_vmcs12)
 		goto out_cached_vmcs12;
 
-	vmx->nested.cached_shadow_vmcs12 = kmalloc(VMCS12_SIZE, GFP_KERNEL);
+	vmx->nested.cached_shadow_vmcs12 = kzalloc(VMCS12_SIZE, GFP_KERNEL);
 	if (!vmx->nested.cached_shadow_vmcs12)
 		goto out_cached_shadow_vmcs12;
 
-- 
2.20.1.97.g81188d93c3-goog