diff options
authorSean Christopherson <sean.j.christopherson@intel.com>2019-01-23 14:39:25 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2019-02-20 22:48:24 +0100
commit34333cc6c2cb021662fd32e24e618d1b86de95bf (patch)
parent8570f9e881e3fde98801bb3a47eef84dd934d405 (diff)
KVM: nVMX: Ignore limit checks on VMX instructions using flat segments
Regarding segments with a limit==0xffffffff, the SDM officially states: When the effective limit is FFFFFFFFH (4 GBytes), these accesses may or may not cause the indicated exceptions. Behavior is implementation-specific and may vary from one execution to another. In practice, all CPUs that support VMX ignore limit checks for "flat segments", i.e. an expand-up data or code segment with base=0 and limit=0xffffffff. This is subtly different than wrapping the effective address calculation based on the address size, as the flat segment behavior also applies to accesses that would wrap the 4g boundary, e.g. a 4-byte access starting at 0xffffffff will access linear addresses 0xffffffff, 0x0, 0x1 and 0x2. Fixes: f9eb4af67c9d ("KVM: nVMX: VMX instructions: add checks for #GP/#SS exceptions") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 files changed, 9 insertions, 3 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 34081cc8cdeb..0050c179c5d3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4087,10 +4087,16 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
/* Protected mode: #GP(0)/#SS(0) if the segment is unusable.
exn = (s.unusable != 0);
- /* Protected mode: #GP(0)/#SS(0) if the memory
- * operand is outside the segment limit.
+ /*
+ * Protected mode: #GP(0)/#SS(0) if the memory operand is
+ * outside the segment limit. All CPUs that support VMX ignore
+ * limit checks for flat segments, i.e. segments with base==0,
+ * limit==0xffffffff and of type expand-up data or code.
- exn = exn || (off + sizeof(u64) > s.limit);
+ if (!(s.base == 0 && s.limit == 0xffffffff &&
+ ((s.type & 8) || !(s.type & 4))))
+ exn = exn || (off + sizeof(u64) > s.limit);
if (exn) {