linux-kernel - [PATCH v2] kvm: x86/vmx: Use kzalloc for cached

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Message-Id: <20190124214820.187794-1-tmroeder@google.com>
Date:   Thu, 24 Jan 2019 13:48:20 -0800
From:   Tom Roeder <tmroeder@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        "Radim Krčmář" <rkrcmar@...hat.com>,
        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: [PATCH v2] 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.

It also changes vmx_get_nested_state to copy out the full 4k VMCS12_SIZE
in copy_to_user rather than only the size of the struct.

Tested: rebuilt against head, booted, and ran the syszkaller repro
  https://syzkaller.appspot.com/text?tag=ReproC&x=174efca3400000 without
  observing any problems.

Reported-by: syzbot+ded1696f6b50b615b630@...kaller.appspotmail.com
Signed-off-by: Tom Roeder <tmroeder@...gle.com>
---
Changelog since v1:
- Changed the copy_to_user calls in vmx_get_nested_state to copy the
  full 4k buffer.

 arch/x86/kvm/vmx/nested.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 2616bd2c7f2c7..ce81539238547 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;
 
@@ -5263,13 +5263,17 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
 			copy_shadow_to_vmcs12(vmx);
 	}
 
-	if (copy_to_user(user_kvm_nested_state->data, vmcs12, sizeof(*vmcs12)))
+	/*
+	 * Copy over the full allocated size of vmcs12 rather than just the size
+	 * of the struct.
+	 */
+	if (copy_to_user(user_kvm_nested_state->data, vmcs12, VMCS12_SIZE))
 		return -EFAULT;
 
 	if (nested_cpu_has_shadow_vmcs(vmcs12) &&
 	    vmcs12->vmcs_link_pointer != -1ull) {
 		if (copy_to_user(user_kvm_nested_state->data + VMCS12_SIZE,
-				 get_shadow_vmcs12(vcpu), sizeof(*vmcs12)))
+				 get_shadow_vmcs12(vcpu), VMCS12_SIZE))
 			return -EFAULT;
 	}
 
-- 
2.20.1.321.g9e740568ce-goog