[Intel-gfx] [PATCH v3 10/28] drm/i915/gvt: Protect gfn hash table with vgpu_lock

Sean Christopherson
2023-05-13T00:36:32Z

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>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
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 117bac85ac2c..0785f9cb2c20 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -351,6 +351,8 @@ __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;
@@ -1552,6 +1554,9 @@ 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) {
@@ -1560,16 +1565,12 @@ 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;
}

@@ -1582,24 +1583,22 @@ 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;
}

@@ -1610,9 +1609,13 @@ 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,
@@ -1624,16 +1627,20 @@ 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;
}
--
2.40.1.606.ga4b1b128d6-goog