[PATCH] x86/hyper-v: Filter non-canonical addresses passed via HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST(_EX)

[Manuel Andreas <manuel.andreas@tum.de>]

In KVM guests with Hyper-V hypercalls enabled, the hypercalls 
HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST and HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX 
allow a guest to request invalidation of portions of a virtual TLB.
For this, the hypercall parameter includes a list of GVAs that are supposed 
to be invalidated.

However, when non-canonical GVAs are passed, there is currently no 
filtering in place and they are eventually passed to checked invocations of 
INVVPID on Intel / INVLPGA on AMD.
While the AMD variant (INVLPGA) will silently ignore the non-canonical 
address and perform a no-op, the Intel variant (INVVPID) will fail and end 
up in invvpid_error, where a WARN_ONCE is triggered:

invvpid failed: ext=0x0 vpid=1 gva=0xaaaaaaaaaaaaa000
WARNING: CPU: 6 PID: 326 at arch/x86/kvm/vmx/vmx.c:482 
invvpid_error+0x91/0xa0 [kvm_intel]
Modules linked in: kvm_intel kvm 9pnet_virtio irqbypass fuse
CPU: 6 UID: 0 PID: 326 Comm: kvm-vm Not tainted 6.15.0 #14 PREEMPT(voluntary)
RIP: 0010:invvpid_error+0x91/0xa0 [kvm_intel]
Call Trace:
  <TASK>
  vmx_flush_tlb_gva+0x320/0x490 [kvm_intel]
  ? __pfx_vmx_flush_tlb_gva+0x10/0x10 [kvm_intel]
  ? kfifo_copy_out+0xcf/0x120
  kvm_hv_vcpu_flush_tlb+0x24f/0x4f0 [kvm]
  ? __pfx_kvm_hv_vcpu_flush_tlb+0x10/0x10 [kvm]
  ? kvm_pmu_is_valid_msr+0x6e/0x80 [kvm]
  ? kvm_get_msr_common+0x219/0x20f0 [kvm]
  kvm_arch_vcpu_ioctl_run+0x3013/0x5810 [kvm]
  /* ... */

Hyper-V documents that invalid GVAs (those that are beyond a partition's 
GVA space) are to be ignored. While not completely clear whether this 
ruling also applies to non-canonical GVAs, it is likely fine to make that 
assumption.

The following patch addresses the issue by skipping non-canonical GVAs 
before calling the architecture-specific invalidation primitive.
I've validated it against a PoC and the issue seems to be fixed.

Signed-off-by: Manuel Andreas <manuel.andreas@tum.de>
Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
  arch/x86/kvm/hyperv.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 24f0318c50d7..644a7aae6dab 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1979,6 +1979,9 @@ int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
  		if (entries[i] == KVM_HV_TLB_FLUSHALL_ENTRY)
  			goto out_flush_all;

+                if (is_noncanonical_invlpg_address(entries[i], vcpu))
+                        continue;
+
  		/*
  		 * Lower 12 bits of 'address' encode the number of additional
  		 * pages to flush.
-- 
2.50.0