diff mbox series

[v3,1/4] KVM: x86: Do not allow use of the MSR filter allow flag in the kernel

Message ID 20220722202303.391709-2-aaronlewis@google.com (mailing list archive)
State New, archived
Headers show
Series MSR filtering / exiting flag cleanup | expand

Commit Message

Aaron Lewis July 22, 2022, 8:23 p.m. UTC
Protect the kernel from using the flag KVM_MSR_FILTER_DEFAULT_ALLOW.
Its value is 0, and using it incorrectly could have unintended
consequences. E.g. prevent someone in the kernel from writing something
like this.

if (filter.flags & KVM_MSR_FILTER_DEFAULT_ALLOW)
        <allow the MSR>

and getting confused when it doesn't work.

It would be more ideal to remove this flag altogether, but userspace
may already be using it, so protecting the kernel is all that can
reasonably be done at this point.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Aaron Lewis <aaronlewis@google.com>

Google's VMM is already using this flag, so we *know* that dropping the
flag entirely will break userspace.  All we can do at this point is
prevent the kernel from using it.

 arch/x86/include/uapi/asm/kvm.h | 2 ++
 1 file changed, 2 insertions(+)
diff mbox series


diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index ee3896416c68..e6dd76c94d47 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -222,7 +222,9 @@  struct kvm_msr_filter_range {
 struct kvm_msr_filter {
+#ifndef __KERNEL__
 #define KVM_MSR_FILTER_DEFAULT_DENY  (1 << 0)
 	__u32 flags;
 	struct kvm_msr_filter_range ranges[KVM_MSR_FILTER_MAX_RANGES];