Reviewed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
On Fri, Mar 10, 2023 at 04:22:41PM -0800, Sean Christopherson wrote:
> 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);
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gvt/kvmgt.c | 55 +++++++++++++++------------
> drivers/gpu/drm/i915/gvt/page_track.c | 10 +----
> 2 files changed, 33 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 68be66395598..9824d075562e 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -366,6 +366,8 @@ __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;
> @@ -1567,6 +1569,9 @@ 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) {
> @@ -1575,16 +1580,12 @@ 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);
> + write_unlock(&kvm->mmu_lock);
> +
> + srcu_read_unlock(&kvm->srcu, idx);
> +
> kvmgt_protect_table_add(info, gfn);
> -
> -out:
> - write_unlock(&kvm->mmu_lock);
> - srcu_read_unlock(&kvm->srcu, idx);
> return 0;
> }
>
> @@ -1597,24 +1598,22 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
> if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, info->status))
> return -ESRCH;
>
> - idx = srcu_read_lock(&kvm->srcu);
> - slot = gfn_to_memslot(kvm, gfn);
> - if (!slot) {
> - srcu_read_unlock(&kvm->srcu, idx);
> - return -EINVAL;
> - }
> -
> - write_lock(&kvm->mmu_lock);
> -
> if (!kvmgt_gfn_is_write_protected(info, gfn))
> - goto out;
> + return 0;
>
> + idx = srcu_read_lock(&kvm->srcu);
> + slot = gfn_to_memslot(kvm, gfn);
> + if (!slot) {
> + srcu_read_unlock(&kvm->srcu, idx);
> + return -EINVAL;
> + }
> +
> + write_lock(&kvm->mmu_lock);
> kvm_slot_page_track_remove_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
> + write_unlock(&kvm->mmu_lock);
> + srcu_read_unlock(&kvm->srcu, idx);
> +
> kvmgt_protect_table_del(info, gfn);
> -
> -out:
> - write_unlock(&kvm->mmu_lock);
> - srcu_read_unlock(&kvm->srcu, idx);
> return 0;
> }
>
> @@ -1625,9 +1624,13 @@ 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,
> @@ -1639,16 +1642,20 @@ 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 df34e73cba41..60a65435556d 100644
> --- 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;
> }
> --
> 2.40.0.rc1.284.g88254d51c5-goog
>
