From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Tom Roeder <tmroeder@google.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"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,
syzbot+ded1696f6b50b615b630@syzkaller.appspotmail.com
Subject: Re: [RFC PATCH] kvm: x86/vmx: Use kzalloc for cached_vmcs12
Date: Mon, 14 Jan 2019 18:43:04 -0800 [thread overview]
Message-ID: <20190115024304.GD5141@linux.intel.com> (raw)
In-Reply-To: <20190114234728.49239-1-tmroeder@google.com>
On Mon, Jan 14, 2019 at 03:47:28PM -0800, Tom Roeder wrote:
> 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.
Is the leak specific to vmx_set_nested_state(), e.g. can we zero out
the memory if copy_from_user() fails instead of taking the hit on every
allocation?
> 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;
Obviously not your code, but why do we allocate VMCS12_SIZE instead of
sizeof(struct vmcs12)? I get why we require userspace to reserve the
full 4k, but I don't understand why KVM needs to allocate the reserved
bytes internally.
> - 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
>
next prev parent reply other threads:[~2019-01-15 2:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-07 1:38 KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page syzbot
2018-11-07 12:10 ` Alexander Potapenko
2018-11-07 12:47 ` Paolo Bonzini
2018-11-07 12:58 ` Liran Alon
2018-11-07 13:37 ` Paolo Bonzini
2019-01-14 23:47 ` [RFC PATCH] kvm: x86/vmx: Use kzalloc for cached_vmcs12 Tom Roeder
2019-01-15 0:03 ` Jim Mattson
2019-01-15 2:43 ` Sean Christopherson [this message]
2019-01-15 10:15 ` Paolo Bonzini
2019-01-23 18:25 ` Tom Roeder
2019-01-24 1:17 ` Paolo Bonzini
2019-01-15 17:51 ` Tom Roeder
2019-01-23 18:33 ` Tom Roeder
2019-01-24 1:18 ` Paolo Bonzini
2019-01-24 21:46 ` Tom Roeder
2018-11-07 12:52 ` KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page Liran Alon
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