Add and use a new mutex, gfn_lock, to protect accesses to the hash table
used to track which gfns are write-protected when shadowing the guest's
GTT. 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@google.com>
---
drivers/gpu/drm/i915/gvt/gvt.h | 1 +
drivers/gpu/drm/i915/gvt/kvmgt.c | 65 ++++++++++++++++++++------------
drivers/gpu/drm/i915/gvt/vgpu.c | 1 +
3 files changed, 43 insertions(+), 24 deletions(-)
diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
index dbf8d7470b2c..fbfd7eafec14 100644
--- a/drivers/gpu/drm/i915/gvt/gvt.h
+++ b/drivers/gpu/drm/i915/gvt/gvt.h
@@ -176,6 +176,7 @@ struct intel_vgpu {
struct vfio_device vfio_device;
struct intel_gvt *gvt;
struct mutex vgpu_lock;
+ struct mutex gfn_lock;
int id;
bool active;
bool attached;
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index ca9926061cd8..a4747e153dad 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->gfn_lock);
+
hash_for_each_possible(info->ptable, p, hnode, gfn) {
if (gfn == p->gfn) {
res = p;
@@ -388,6 +390,8 @@ static void kvmgt_protect_table_add(struct intel_vgpu *info, gfn_t gfn)
{
struct kvmgt_pgfn *p;
+ lockdep_assert_held(&info->gfn_lock);
+
if (kvmgt_gfn_is_write_protected(info, gfn))
return;
@@ -1563,60 +1567,68 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
{
struct kvm *kvm = info->vfio_device.kvm;
struct kvm_memory_slot *slot;
- int idx;
+ int idx, ret = 0;
if (!info->attached)
return -ESRCH;
+ mutex_lock(&info->gfn_lock);
+
+ if (kvmgt_gfn_is_write_protected(info, gfn))
+ goto out;
+
idx = srcu_read_lock(&kvm->srcu);
slot = gfn_to_memslot(kvm, gfn);
if (!slot) {
srcu_read_unlock(&kvm->srcu, idx);
- return -EINVAL;
+ ret = -EINVAL;
+ goto out;
}
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;
+ mutex_unlock(&info->gfn_lock);
+ return ret;
}
int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
{
struct kvm *kvm = info->vfio_device.kvm;
struct kvm_memory_slot *slot;
- int idx;
+ int idx, ret = 0;
if (!info->attached)
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);
+ mutex_lock(&info->gfn_lock);
if (!kvmgt_gfn_is_write_protected(info, gfn))
goto out;
+ idx = srcu_read_lock(&kvm->srcu);
+ slot = gfn_to_memslot(kvm, gfn);
+ if (!slot) {
+ srcu_read_unlock(&kvm->srcu, idx);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ 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;
+ mutex_unlock(&info->gfn_lock);
+ return ret;
}
static void kvmgt_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
@@ -1627,11 +1639,13 @@ static void kvmgt_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
container_of(node, struct intel_vgpu, track_node);
mutex_lock(&info->vgpu_lock);
+ mutex_lock(&info->gfn_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->gfn_lock);
mutex_unlock(&info->vgpu_lock);
}
@@ -1644,16 +1658,19 @@ 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->gfn_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->gfn_lock);
}
void intel_vgpu_detach_regions(struct intel_vgpu *vgpu)
diff --git a/drivers/gpu/drm/i915/gvt/vgpu.c b/drivers/gpu/drm/i915/gvt/vgpu.c
index 56c71474008a..f2479781b770 100644
--- a/drivers/gpu/drm/i915/gvt/vgpu.c
+++ b/drivers/gpu/drm/i915/gvt/vgpu.c
@@ -277,6 +277,7 @@ struct intel_vgpu *intel_gvt_create_idle_vgpu(struct intel_gvt *gvt)
vgpu->id = IDLE_VGPU_IDR;
vgpu->gvt = gvt;
mutex_init(&vgpu->vgpu_lock);
+ mutex_init(&vgpu->gfn_lock);
for (i = 0; i < I915_NUM_ENGINES; i++)
INIT_LIST_HEAD(&vgpu->submission.workload_q_head[i]);
--
2.39.0.314.g84b9a713c41-googOn Fri, Dec 23, 2022 at 12:57:21AM +0000, Sean Christopherson wrote:
> Add and use a new mutex, gfn_lock, to protect accesses to the hash table
> used to track which gfns are write-protected when shadowing the guest's
> GTT. 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);
>
This gfn_lock could lead to deadlock in below sequence.
(1) kvm_write_track_add_gfn() to GFN 1
(2) kvmgt_page_track_write() for GFN 1
kvmgt_page_track_write()
|
|->mutex_lock(&info->vgpu_lock)
|->intel_vgpu_page_track_handler (as is kvmgt_gfn_is_write_protected)
|
|->page_track->handler() (ppgtt_write_protection_handler())
|
|->ppgtt_handle_guest_write_page_table_bytes()
|
|->ppgtt_handle_guest_write_page_table()
|
|->ppgtt_handle_guest_entry_add() --> new_present
|
|->ppgtt_populate_spt_by_guest_entry()
|
|->intel_vgpu_enable_page_track() --> for GFN 2
|
|->intel_gvt_page_track_add()
|
|->mutex_lock(&info->gfn_lock) ===>deadlock
Below fix based on this patch is to reuse vgpu_lock to protect the hash table
info->ptable.
Please check if it's good.
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index b924ed079ad4..526bd973e784 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -364,7 +364,7 @@ __kvmgt_protect_table_find(struct intel_vgpu *info, gfn_t gfn)
{
struct kvmgt_pgfn *p, *res = NULL;
- lockdep_assert_held(&info->gfn_lock);
+ lockdep_assert_held(&info->vgpu_lock);
hash_for_each_possible(info->ptable, p, hnode, gfn) {
if (gfn == p->gfn) {
@@ -388,7 +388,7 @@ static void kvmgt_protect_table_add(struct intel_vgpu *info, gfn_t gfn)
{
struct kvmgt_pgfn *p;
- lockdep_assert_held(&info->gfn_lock);
+ lockdep_assert_held(&info->vgpu_lock);
if (kvmgt_gfn_is_write_protected(info, gfn))
return;
@@ -1572,7 +1572,7 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
if (!info->attached)
return -ESRCH;
- mutex_lock(&info->gfn_lock);
+ lockdep_assert_held(&info->vgpu_lock);
if (kvmgt_gfn_is_write_protected(info, gfn))
goto out;
@@ -1581,7 +1581,6 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
if (!ret)
kvmgt_protect_table_add(info, gfn);
out:
- mutex_unlock(&info->gfn_lock);
return ret;
}
@@ -1592,7 +1591,7 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
if (!info->attached)
return 0;
- mutex_lock(&info->gfn_lock);
+ lockdep_assert_held(&info->vgpu_lock);
if (!kvmgt_gfn_is_write_protected(info, gfn))
goto out;
@@ -1601,7 +1600,6 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
if (!ret)
kvmgt_protect_table_del(info, gfn);
out:
- mutex_unlock(&info->gfn_lock);
return ret;
}
@@ -1612,13 +1610,15 @@ static void kvmgt_page_track_write(gpa_t gpa, const u8 *val, int len,
container_of(node, struct intel_vgpu, track_node);
mutex_lock(&info->vgpu_lock);
- mutex_lock(&info->gfn_lock);
if (kvmgt_gfn_is_write_protected(info, gpa >> PAGE_SHIFT))
intel_vgpu_page_track_handler(info, gpa,
(void *)val, len);
}
- mutex_unlock(&info->gfn_lock);
mutex_unlock(&info->vgpu_lock);
}
@@ -1629,12 +1629,11 @@ static void kvmgt_page_track_remove_region(gfn_t gfn, unsigned long nr_pages,
struct intel_vgpu *info =
container_of(node, struct intel_vgpu, track_node);
- mutex_lock(&info->gfn_lock);
+ lockdep_assert_held(&info->vgpu_lock);
for (i = 0; i < nr_pages; i++) {
if (kvmgt_gfn_is_write_protected(info, gfn + i))
kvmgt_protect_table_del(info, gfn + i);
}
- mutex_unlock(&info->gfn_lock);
}
Thanks
Yan
On Wed, Dec 28, 2022, Yan Zhao wrote:
> On Fri, Dec 23, 2022 at 12:57:21AM +0000, Sean Christopherson wrote:
> > Add and use a new mutex, gfn_lock, to protect accesses to the hash table
> > used to track which gfns are write-protected when shadowing the guest's
> > GTT. 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);
> >
> This gfn_lock could lead to deadlock in below sequence.
>
> (1) kvm_write_track_add_gfn() to GFN 1
> (2) kvmgt_page_track_write() for GFN 1
> kvmgt_page_track_write()
> |
> |->mutex_lock(&info->vgpu_lock)
> |->intel_vgpu_page_track_handler (as is kvmgt_gfn_is_write_protected)
> |
> |->page_track->handler() (ppgtt_write_protection_handler())
> |
> |->ppgtt_handle_guest_write_page_table_bytes()
> |
> |->ppgtt_handle_guest_write_page_table()
> |
> |->ppgtt_handle_guest_entry_add() --> new_present
> |
> |->ppgtt_populate_spt_by_guest_entry()
> |
> |->intel_vgpu_enable_page_track() --> for GFN 2
> |
> |->intel_gvt_page_track_add()
> |
> |->mutex_lock(&info->gfn_lock) ===>deadlock
Or even more simply,
kvmgt_page_track_write()
|
-> intel_vgpu_page_track_handler()
|
-> intel_gvt_page_track_remove()
>
> Below fix based on this patch is to reuse vgpu_lock to protect the hash table
> info->ptable.
> Please check if it's good.
>
>
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index b924ed079ad4..526bd973e784 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -364,7 +364,7 @@ __kvmgt_protect_table_find(struct intel_vgpu *info, gfn_t gfn)
> {
> struct kvmgt_pgfn *p, *res = NULL;
>
> - lockdep_assert_held(&info->gfn_lock);
> + lockdep_assert_held(&info->vgpu_lock);
>
> hash_for_each_possible(info->ptable, p, hnode, gfn) {
> if (gfn == p->gfn) {
> @@ -388,7 +388,7 @@ static void kvmgt_protect_table_add(struct intel_vgpu *info, gfn_t gfn)
> {
> struct kvmgt_pgfn *p;
>
> - lockdep_assert_held(&info->gfn_lock);
> + lockdep_assert_held(&info->vgpu_lock);
I'll just delete these assertions, the one in __kvmgt_protect_table_find() should
cover everything and is ultimately the assert that matters.
> @@ -1629,12 +1629,11 @@ static void kvmgt_page_track_remove_region(gfn_t gfn, unsigned long nr_pages,
> struct intel_vgpu *info =
> container_of(node, struct intel_vgpu, track_node);
>
> - mutex_lock(&info->gfn_lock);
> + lockdep_assert_held(&info->vgpu_lock);
This path needs to manually take vgpu_lock as it's called from KVM. IIRC, this
is the main reason I tried adding a new lock. That and I had a hell of a time
figuring out whether or not vgpu_lock would actually be held.
Looking at this with fresh eyes, AFAICT intel_vgpu_reset_gtt() is the only other
path that can reach __kvmgt_protect_table_find() without holding vgpu_lock, by
way of intel_gvt_page_track_remove(). But unless there's magic I'm missing, that's
dead code and can simply be deleted.
On Tue, Jan 03, 2023 at 08:43:17PM +0000, Sean Christopherson wrote:
> On Wed, Dec 28, 2022, Yan Zhao wrote:
> > On Fri, Dec 23, 2022 at 12:57:21AM +0000, Sean Christopherson wrote:
> > > Add and use a new mutex, gfn_lock, to protect accesses to the hash table
> > > used to track which gfns are write-protected when shadowing the guest's
> > > GTT. 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);
> > >
> > This gfn_lock could lead to deadlock in below sequence.
> >
> > (1) kvm_write_track_add_gfn() to GFN 1
> > (2) kvmgt_page_track_write() for GFN 1
> > kvmgt_page_track_write()
> > |
> > |->mutex_lock(&info->vgpu_lock)
> > |->intel_vgpu_page_track_handler (as is kvmgt_gfn_is_write_protected)
> > |
> > |->page_track->handler() (ppgtt_write_protection_handler())
> > |
> > |->ppgtt_handle_guest_write_page_table_bytes()
> > |
> > |->ppgtt_handle_guest_write_page_table()
> > |
> > |->ppgtt_handle_guest_entry_add() --> new_present
> > |
> > |->ppgtt_populate_spt_by_guest_entry()
> > |
> > |->intel_vgpu_enable_page_track() --> for GFN 2
> > |
> > |->intel_gvt_page_track_add()
> > |
> > |->mutex_lock(&info->gfn_lock) ===>deadlock
>
> Or even more simply,
>
> kvmgt_page_track_write()
> |
> -> intel_vgpu_page_track_handler()
> |
> -> intel_gvt_page_track_remove()
>
yes.
> >
> > Below fix based on this patch is to reuse vgpu_lock to protect the hash table
> > info->ptable.
> > Please check if it's good.
> >
> >
> > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > index b924ed079ad4..526bd973e784 100644
> > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > @@ -364,7 +364,7 @@ __kvmgt_protect_table_find(struct intel_vgpu *info, gfn_t gfn)
> > {
> > struct kvmgt_pgfn *p, *res = NULL;
> >
> > - lockdep_assert_held(&info->gfn_lock);
> > + lockdep_assert_held(&info->vgpu_lock);
> >
> > hash_for_each_possible(info->ptable, p, hnode, gfn) {
> > if (gfn == p->gfn) {
> > @@ -388,7 +388,7 @@ static void kvmgt_protect_table_add(struct intel_vgpu *info, gfn_t gfn)
> > {
> > struct kvmgt_pgfn *p;
> >
> > - lockdep_assert_held(&info->gfn_lock);
> > + lockdep_assert_held(&info->vgpu_lock);
>
> I'll just delete these assertions, the one in __kvmgt_protect_table_find() should
> cover everything and is ultimately the assert that matters.
>
> > @@ -1629,12 +1629,11 @@ static void kvmgt_page_track_remove_region(gfn_t gfn, unsigned long nr_pages,
> > struct intel_vgpu *info =
> > container_of(node, struct intel_vgpu, track_node);
> >
> > - mutex_lock(&info->gfn_lock);
> > + lockdep_assert_held(&info->vgpu_lock);
>
> This path needs to manually take vgpu_lock as it's called from KVM. IIRC, this
> is the main reason I tried adding a new lock. That and I had a hell of a time
> figuring out whether or not vgpu_lock would actually be held.
Right. In the path of kvmgt_page_track_remove_region(),
mutex_lock(&info->vgpu_lock) and mutex_unlock(&info->vgpu_lock) are
required.
static void kvmgt_page_track_remove_region(gfn_t gfn, unsigned long nr_pages,
struct kvm_page_track_notifier_node *node)
{
unsigned long i;
struct intel_vgpu *info =
container_of(node, struct intel_vgpu, track_node);
mutex_lock(&info->vgpu_lock);
for (i = 0; i < nr_pages; i++) {
if (kvmgt_gfn_is_write_protected(info, gfn + i))
kvmgt_protect_table_del(info, gfn + i);
}
mutex_unlock(&info->vgpu_lock);
}
The reason I previously could have lockdep_assert_held(&info->vgpu_lock) passed
is that I didn't get LOCKDEP configured, so it's basically a void.
(sorry, though I actually also called mutex_is_locked(&info->vcpu_lock)
in some paths to check lockdep_assert_held() worked properly. But it's my
fault not to double check it's compiled correctly).
>
> Looking at this with fresh eyes, AFAICT intel_vgpu_reset_gtt() is the only other
> path that can reach __kvmgt_protect_table_find() without holding vgpu_lock, by
> way of intel_gvt_page_track_remove(). But unless there's magic I'm missing, that's
> dead code and can simply be deleted.
Yes, I found intel_vgpu_reset_gtt() has not been called since
ba25d977571e1551b7032d6104e49efd6f88f8ad.
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