korg/linux
0
0
Fork 0
mirror of https://mirrors.bfsu.edu.cn/git/linux.git synced 2024-11-11 12:28:41 +08:00
Code Issues Packages Projects Releases Wiki Activity

KVM: VMX: Forbid userspace MSR filters for x2APIC

Browse Source 
Allowing userspace to intercept reads to x2APIC MSRs when APICV is
fully enabled for the guest simply can't work.   But more in general,
the LAPIC could be set to in-kernel after the MSR filter is setup
and allowing accesses by userspace would be very confusing.

We could in principle allow userspace to intercept reads and writes to TPR,
and writes to EOI and SELF_IPI, but while that could be made it work, it
would still be silly.

Cc: Alexander Graf <graf@amazon.com>
Cc: Aaron Lewis <aaronlewis@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2020-10-20 10:57:01 -04:00
parent 9389b9d5d3
commit 043248b328
2 changed files with 18 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
Documentation/virt/kvm/api.rst
View File

@ -4777,20 +4777,22 @@ specify whether a certain MSR access should be explicitly filtered for or not.
If this ioctl has never been invoked, MSR accesses are not guarded and the
default KVM in-kernel emulation behavior is fully preserved.
Calling this ioctl with an empty set of ranges (all nmsrs == 0) disables MSR
filtering. In that mode, ``KVM_MSR_FILTER_DEFAULT_DENY`` is invalid and causes
an error.
As soon as the filtering is in place, every MSR access is processed through
the filtering except for accesses to the x2APIC MSRs (from 0x800 to 0x8ff);
x2APIC MSRs are always allowed, independent of the ``default_allow`` setting,
and their behavior depends on the ``X2APIC_ENABLE`` bit of the APIC base
register.
If a bit is within one of the defined ranges, read and write
accesses are guarded by the bitmap's value for the MSR index. If it is not
defined in any range, whether MSR access is rejected is determined by the flags
field in the kvm_msr_filter struct: ``KVM_MSR_FILTER_DEFAULT_ALLOW`` and
``KVM_MSR_FILTER_DEFAULT_DENY``.
Calling this ioctl with an empty set of ranges (all nmsrs == 0) disables MSR
filtering. In that mode, KVM_MSR_FILTER_DEFAULT_DENY no longer has any effect.
If a bit is within one of the defined ranges, read and write accesses are
guarded by the bitmap's value for the MSR index if the kind of access
is included in the ``struct kvm_msr_filter_range`` flags. If no range
cover this particular access, the behavior is determined by the flags
field in the kvm_msr_filter struct: ``KVM_MSR_FILTER_DEFAULT_ALLOW``
and ``KVM_MSR_FILTER_DEFAULT_DENY``.
Each bitmap range specifies a range of MSRs to potentially allow access on.
The range goes from MSR index [base .. base+nmsrs]. The flags field

9
arch/x86/kvm/x86.c
View File

@ -5252,14 +5252,21 @@ static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm, void __user *argp)
struct kvm_msr_filter filter;
bool default_allow;
int r = 0;
bool empty = true;
u32 i;
if (copy_from_user(&filter, user_msr_filter, sizeof(filter)))
return -EFAULT;
kvm_clear_msr_filter(kvm);
for (i = 0; i < ARRAY_SIZE(filter.ranges); i++)
empty &= !filter.ranges[i].nmsrs;
default_allow = !(filter.flags & KVM_MSR_FILTER_DEFAULT_DENY);
if (empty && !default_allow)
return -EINVAL;
kvm_clear_msr_filter(kvm);
kvm->arch.msr_filter.default_allow = default_allow;
/*