From: Paolo Bonzini <pbonzini@redhat.com>
To: Alexander Potapenko <glider@google.com>,
syzbot+ded1696f6b50b615b630@syzkaller.appspotmail.com
Cc: kvm@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
rkrcmar@redhat.com, syzkaller-bugs@googlegroups.com
Subject: Re: KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page
Date: Wed, 7 Nov 2018 13:47:58 +0100 [thread overview]
Message-ID: <9d2e26fb-1d2a-248f-5451-ee95d8a6c017@redhat.com> (raw)
In-Reply-To: <CAG_fn=Wmc+YU8BMcY_RXxAvVTpAMez5QUFyQSH3UsRg4Y-ZwMQ@mail.gmail.com>
On 07/11/2018 13:10, Alexander Potapenko wrote:
> This appears to be a real bug in KVM.
> Please see a simplified reproducer attached.
Thanks, I agree it's a reael bug. The basic issue is that the
kvm_state->size member is too small (1040) in the KVM_SET_NESTED_STATE
ioctl, aka 0x4080aebf.
One way to fix it would be to just change kmalloc to kzalloc when
allocating cached_vmcs12 and cached_shadow_vmcs12, but really the ioctl
is wrong and should be rejected. And the case where a shadow VMCS has
to be loaded is even more wrong, and we have to fix it anyway, so I
don't really like the idea of papering over the bug in the allocation.
I'll test this patch and submit it formally:
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c645f777b425..c546f0b1f3e0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -14888,10 +14888,13 @@ static int vmx_set_nested_state(struct
kvm_vcpu *vcpu,
if (ret)
return ret;
- /* Empty 'VMXON' state is permitted */
- if (kvm_state->size < sizeof(kvm_state) + sizeof(*vmcs12))
+ /* Empty 'VMXON' state is permitted. A partial VMCS12 is not. */
+ if (kvm_state->size == sizeof(kvm_state))
return 0;
+ if (kvm_state->size < sizeof(kvm_state) + VMCS12_SIZE)
+ return -EINVAL;
+
if (kvm_state->vmx.vmcs_pa != -1ull) {
if (kvm_state->vmx.vmcs_pa == kvm_state->vmx.vmxon_pa ||
!page_address_valid(vcpu, kvm_state->vmx.vmcs_pa))
@@ -14917,6 +14920,7 @@ static int vmx_set_nested_state(struct kvm_vcpu
*vcpu,
}
vmcs12 = get_vmcs12(vcpu);
+ BUILD_BUG_ON(sizeof(*vmcs12) > VMCS12_SIZE);
if (copy_from_user(vmcs12, user_kvm_nested_state->data, sizeof(*vmcs12)))
return -EFAULT;
@@ -14932,7 +14936,7 @@ static int vmx_set_nested_state(struct kvm_vcpu
*vcpu,
if (nested_cpu_has_shadow_vmcs(vmcs12) &&
vmcs12->vmcs_link_pointer != -1ull) {
struct vmcs12 *shadow_vmcs12 = get_shadow_vmcs12(vcpu);
- if (kvm_state->size < sizeof(kvm_state) + 2 * sizeof(*vmcs12))
+ if (kvm_state->size < sizeof(kvm_state) + 2 * VMCS12_SIZE)
return -EINVAL;
if (copy_from_user(shadow_vmcs12,
Paolo
next prev parent reply other threads:[~2018-11-07 12:48 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 [this message]
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
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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