linux-kernel - [RFC PATCH] kvm: x86/vmx: Use kzalloc for cached

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Message-Id: <20190114234728.49239-1-tmroeder@google.com>
Date:   Mon, 14 Jan 2019 15:47:28 -0800
From:   Tom Roeder <tmroeder@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "Radim Krčmář" <rkrcmar@...hat.com>
Cc:     Liran Alon <liran.alon@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Roeder <tmroeder@...gle.com>,
        syzbot+ded1696f6b50b615b630@...kaller.appspotmail.com
Subject: [RFC PATCH] kvm: x86/vmx: Use kzalloc for cached_vmcs12

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@...kaller.appspotmail.com
Signed-off-by: Tom Roeder <tmroeder@...gle.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