drm/i915/gvt: Protect gfn hash table with vgpu_lock

Use vgpu_lock instead of KVM's mmu_lock to protect accesses to the hash
table used to track which gfns are write-protected when shadowing the
guest's GTT, and hoist the acquisition of vgpu_lock from
intel_vgpu_page_track_handler() out to its sole caller,
kvmgt_page_track_write().

This fixes a bug where kvmgt_page_track_write(), which doesn't hold
kvm->mmu_lock, could race with intel_gvt_page_track_remove() and trigger
a use-after-free.

Fixing kvmgt_page_track_write() by taking kvm->mmu_lock is not an option
as mmu_lock is a r/w spinlock, and intel_vgpu_page_track_handler() might
sleep when acquiring vgpu->cache_lock deep down the callstack:

  intel_vgpu_page_track_handler()
  |
  |->  page_track->handler / ppgtt_write_protection_handler()
       |
       |-> ppgtt_handle_guest_write_page_table_bytes()
           |
           |->  ppgtt_handle_guest_write_page_table()
                |
                |-> ppgtt_handle_guest_entry_removal()
                    |
                    |-> ppgtt_invalidate_pte()
                        |
                        |-> intel_gvt_dma_unmap_guest_page()
                            |
                            |-> mutex_lock(&vgpu->cache_lock);

Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Link: https://lore.kernel.org/r/20230729013535.1070024-12-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 6f52886c405179b3545442ac4f7c5342a3aed408..034be0655daa7205c758ccc44aaca1feeb994742 100644 (file)
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -352,6 +352,8 @@ __kvmgt_protect_table_find(struct intel_vgpu *info, gfn_t gfn)
 {
        struct kvmgt_pgfn *p, *res = NULL;
 
+       lockdep_assert_held(&info->vgpu_lock);
+
        hash_for_each_possible(info->ptable, p, hnode, gfn) {
                if (gfn == p->gfn) {
                        res = p;
@@ -1553,6 +1555,9 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
        if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, info->status))
                return -ESRCH;
 
+       if (kvmgt_gfn_is_write_protected(info, gfn))
+               return 0;
+
        idx = srcu_read_lock(&kvm->srcu);
        slot = gfn_to_memslot(kvm, gfn);
        if (!slot) {
@@ -1561,16 +1566,12 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
        }
 
        write_lock(&kvm->mmu_lock);
-
-       if (kvmgt_gfn_is_write_protected(info, gfn))
-               goto out;
-
        kvm_slot_page_track_add_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
-       kvmgt_protect_table_add(info, gfn);
-
-out:
        write_unlock(&kvm->mmu_lock);
+
        srcu_read_unlock(&kvm->srcu, idx);
+
+       kvmgt_protect_table_add(info, gfn);
        return 0;
 }
 
@@ -1583,6 +1584,9 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
        if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, info->status))
                return -ESRCH;
 
+       if (!kvmgt_gfn_is_write_protected(info, gfn))
+               return 0;
+
        idx = srcu_read_lock(&kvm->srcu);
        slot = gfn_to_memslot(kvm, gfn);
        if (!slot) {
@@ -1591,16 +1595,11 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
        }
 
        write_lock(&kvm->mmu_lock);
-
-       if (!kvmgt_gfn_is_write_protected(info, gfn))
-               goto out;
-
        kvm_slot_page_track_remove_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
-       kvmgt_protect_table_del(info, gfn);
-
-out:
        write_unlock(&kvm->mmu_lock);
        srcu_read_unlock(&kvm->srcu, idx);
+
+       kvmgt_protect_table_del(info, gfn);
        return 0;
 }
 
@@ -1611,9 +1610,13 @@ static void kvmgt_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
        struct intel_vgpu *info =
                container_of(node, struct intel_vgpu, track_node);
 
+       mutex_lock(&info->vgpu_lock);
+
        if (kvmgt_gfn_is_write_protected(info, gpa_to_gfn(gpa)))
                intel_vgpu_page_track_handler(info, gpa,
                                                     (void *)val, len);
+
+       mutex_unlock(&info->vgpu_lock);
 }
 
 static void kvmgt_page_track_flush_slot(struct kvm *kvm,
@@ -1625,16 +1628,20 @@ static void kvmgt_page_track_flush_slot(struct kvm *kvm,
        struct intel_vgpu *info =
                container_of(node, struct intel_vgpu, track_node);
 
-       write_lock(&kvm->mmu_lock);
+       mutex_lock(&info->vgpu_lock);
+
        for (i = 0; i < slot->npages; i++) {
                gfn = slot->base_gfn + i;
                if (kvmgt_gfn_is_write_protected(info, gfn)) {
+                       write_lock(&kvm->mmu_lock);
                        kvm_slot_page_track_remove_page(kvm, slot, gfn,
                                                KVM_PAGE_TRACK_WRITE);
+                       write_unlock(&kvm->mmu_lock);
+
                        kvmgt_protect_table_del(info, gfn);
                }
        }
-       write_unlock(&kvm->mmu_lock);
+       mutex_unlock(&info->vgpu_lock);
 }
 
 void intel_vgpu_detach_regions(struct intel_vgpu *vgpu)

diff --git a/drivers/gpu/drm/i915/gvt/page_track.c b/drivers/gpu/drm/i915/gvt/page_track.c
index df34e73cba41a4d492761403dfac54fbbf478563..60a65435556dc9e6d7e2cd1812b8ca16dd9ab2f1 100644 (file)
--- a/drivers/gpu/drm/i915/gvt/page_track.c
+++ b/drivers/gpu/drm/i915/gvt/page_track.c
@@ -162,13 +162,9 @@ int intel_vgpu_page_track_handler(struct intel_vgpu *vgpu, u64 gpa,
        struct intel_vgpu_page_track *page_track;
        int ret = 0;
 
-       mutex_lock(&vgpu->vgpu_lock);
-
        page_track = intel_vgpu_find_page_track(vgpu, gpa >> PAGE_SHIFT);
-       if (!page_track) {
-               ret = -ENXIO;
-               goto out;
-       }
+       if (!page_track)
+               return -ENXIO;
 
        if (unlikely(vgpu->failsafe)) {
                /* Remove write protection to prevent furture traps. */
@@ -179,7 +175,5 @@ int intel_vgpu_page_track_handler(struct intel_vgpu *vgpu, u64 gpa,
                        gvt_err("guest page write error, gpa %llx\n", gpa);
        }
 
-out:
-       mutex_unlock(&vgpu->vgpu_lock);
        return ret;
 }