[kernel,v4,2/2] KVM: PPC: Check if IOMMU page is contained in the pinned physical page

Message ID 20180705080133.18690-3-aik@ozlabs.ru
State Superseded
Headers show
Series
  • KVM: PPC: Check if IOMMU page is contained in the pinned physical page
Related show

Commit Message

Alexey Kardashevskiy July 5, 2018, 8:01 a.m.
A VM which has:
 - a DMA capable device passed through to it (eg. network card);
 - running a malicious kernel that ignores H_PUT_TCE failure;
 - capability of using IOMMU pages bigger that physical pages
can create an IOMMU mapping that exposes (for example) 16MB of
the host physical memory to the device when only 64K was allocated to
the VM.

The remaining 16MB - 64K will be some other content of host memory,
possibly including pages of the VM, but also pages of host kernel memory,
host programs or other VMs.

The attacking VM does not control the location of the page it can map,
and is only allowed to map as many pages as it has pages of RAM.

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory; however this check is missing in
the KVM fastpath (H_PUT_TCE accelerated code). We were lucky so far and
did not hit this yet as the very first time when the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver, this fails and
the guest does not retry,

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size. This calculates maximum page size as a minimum of
the natural region alignment and compound page size.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v4:
* reimplemented max pageshift calculation

v3:
* fixed upper limit for the page size
* added checks that we don't register parts of a huge page

v2:
* explicitely check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for /pci@800000020000000/ethernet@0: -1
---
 arch/powerpc/include/asm/mmu_context.h |  4 ++--
 arch/powerpc/kvm/book3s_64_vio.c       |  2 +-
 arch/powerpc/kvm/book3s_64_vio_hv.c    |  6 ++++--
 arch/powerpc/mm/mmu_context_iommu.c    | 23 ++++++++++++++++++++---
 drivers/vfio/vfio_iommu_spapr_tce.c    |  2 +-
 5 files changed, 28 insertions(+), 9 deletions(-)

Comments

David Gibson July 6, 2018, 5:13 a.m. | #1
On Thu, Jul 05, 2018 at 06:01:33PM +1000, Alexey Kardashevskiy wrote:
> A VM which has:
>  - a DMA capable device passed through to it (eg. network card);
>  - running a malicious kernel that ignores H_PUT_TCE failure;
>  - capability of using IOMMU pages bigger that physical pages
> can create an IOMMU mapping that exposes (for example) 16MB of
> the host physical memory to the device when only 64K was allocated to
> the VM.
> 
> The remaining 16MB - 64K will be some other content of host memory,
> possibly including pages of the VM, but also pages of host kernel memory,
> host programs or other VMs.
> 
> The attacking VM does not control the location of the page it can map,
> and is only allowed to map as many pages as it has pages of RAM.
> 
> We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
> an IOMMU page is contained in the physical page so the PCI hardware won't
> get access to unassigned host memory; however this check is missing in
> the KVM fastpath (H_PUT_TCE accelerated code). We were lucky so far and
> did not hit this yet as the very first time when the mapping happens
> we do not have tbl::it_userspace allocated yet and fall back to
> the userspace which in turn calls VFIO IOMMU driver, this fails and
> the guest does not retry,
> 
> This stores the smallest preregistered page size in the preregistered
> region descriptor and changes the mm_iommu_xxx API to check this against
> the IOMMU page size. This calculates maximum page size as a minimum of
> the natural region alignment and compound page size.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

It's certainly better than what we have, though a couple of comments
still:

[snip]
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> index abb4364..11e1029 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -27,6 +27,7 @@ struct mm_iommu_table_group_mem_t {
>  	struct rcu_head rcu;
>  	unsigned long used;
>  	atomic64_t mapped;
> +	unsigned int pageshift;
>  	u64 ua;			/* userspace address */
>  	u64 entries;		/* number of entries in hpas[] */
>  	u64 *hpas;		/* vmalloc'ed */
> @@ -125,7 +126,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  {
>  	struct mm_iommu_table_group_mem_t *mem;
>  	long i, j, ret = 0, locked_entries = 0;
> -	struct page *page = NULL;
> +	unsigned int pageshift;
> +	struct page *page = NULL, *head = NULL;
>  
>  	mutex_lock(&mem_list_mutex);
>  
> @@ -159,6 +161,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  		goto unlock_exit;
>  	}
>  
> +	mem->pageshift = __builtin_ctzl(ua | (entries << PAGE_SHIFT));

This could definitely do with a comment saying what this is trying to
calculate.

Explicitly calling a _builtin_ is also kinda horrid.  I wrote my
sample thinking of qemu where there's a standard and widely used
ctz64().  Not sure if there's something else we should be using in kernelspace.

>  	mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0])));
>  	if (!mem->hpas) {
>  		kfree(mem);
> @@ -199,9 +202,17 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  			}
>  		}
>  populate:
> +		pageshift = PAGE_SHIFT;
> +		if (PageCompound(page))
> +			pageshift += compound_order(compound_head(page));

So, as I said in reply to the earlier version, I'm not 100% sure there
isn't some way a compound_page could end up mapped unaligned in
userspace (with smaller userspace mappings of a larger underlying
physical page).  A WARN_ON() and fallback to assuming pageshift =
PAGE_SHIFT in that case would probably be a good idea.

> +		mem->pageshift = min(mem->pageshift, pageshift);
>  		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
>  	}
>  
> +	/* We have an incomplete huge page, default to PAGE_SHIFT */
> +	if (head)
> +		mem->pageshift = PAGE_SHIFT;
> +
>  	atomic64_set(&mem->mapped, 1);
>  	mem->used = 1;
>  	mem->ua = ua;
> @@ -349,7 +360,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
>  EXPORT_SYMBOL_GPL(mm_iommu_find);
>  
>  long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
> -		unsigned long ua, unsigned long *hpa)
> +		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
>  {
>  	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
>  	u64 *va = &mem->hpas[entry];
> @@ -357,6 +368,9 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
>  	if (entry >= mem->entries)
>  		return -EFAULT;
>  
> +	if (pageshift > mem->pageshift)
> +		return -EFAULT;
> +
>  	*hpa = *va | (ua & ~PAGE_MASK);
>  
>  	return 0;
> @@ -364,7 +378,7 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
>  EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
>  
>  long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
> -		unsigned long ua, unsigned long *hpa)
> +		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
>  {
>  	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
>  	void *va = &mem->hpas[entry];
> @@ -373,6 +387,9 @@ long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
>  	if (entry >= mem->entries)
>  		return -EFAULT;
>  
> +	if (pageshift > mem->pageshift)
> +		return -EFAULT;
> +
>  	pa = (void *) vmalloc_to_phys(va);
>  	if (!pa)
>  		return -EFAULT;
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 2da5f05..7cd63b0 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -467,7 +467,7 @@ static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
>  	if (!mem)
>  		return -EINVAL;
>  
> -	ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
> +	ret = mm_iommu_ua_to_hpa(mem, tce, shift, phpa);
>  	if (ret)
>  		return -EINVAL;
>
Michael Ellerman July 6, 2018, 6 a.m. | #2
Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> index abb4364..11e1029 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -159,6 +161,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  		goto unlock_exit;
>  	}
>  
> +	mem->pageshift = __builtin_ctzl(ua | (entries << PAGE_SHIFT));

__builtin_ctzl(0) is undefined, so are we guaranteed that
(ua | (entries << PAGE_SHIFT)) is never zero? I couldn't convince
myself.

> @@ -199,9 +202,17 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  			}
>  		}
>  populate:
> +		pageshift = PAGE_SHIFT;
> +		if (PageCompound(page))
> +			pageshift += compound_order(compound_head(page));
> +		mem->pageshift = min(mem->pageshift, pageshift);
>  		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
>  	}
>  
> +	/* We have an incomplete huge page, default to PAGE_SHIFT */
> +	if (head)
> +		mem->pageshift = PAGE_SHIFT;
> +

You never set head AFIACS? (other than in the initialiser)

cheers
David Gibson July 6, 2018, 6:15 a.m. | #3
On Fri, Jul 06, 2018 at 04:00:30PM +1000, Michael Ellerman wrote:
> Alexey Kardashevskiy <aik@ozlabs.ru> writes:
> 
> > diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> > index abb4364..11e1029 100644
> > --- a/arch/powerpc/mm/mmu_context_iommu.c
> > +++ b/arch/powerpc/mm/mmu_context_iommu.c
> > @@ -159,6 +161,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
> >  		goto unlock_exit;
> >  	}
> >  
> > +	mem->pageshift = __builtin_ctzl(ua | (entries << PAGE_SHIFT));
> 
> __builtin_ctzl(0) is undefined, so are we guaranteed that
> (ua | (entries << PAGE_SHIFT)) is never zero? I couldn't convince
> myself.

We certainly don't need to care about that case, since registering a
zero-length region (entries == 0) is no-op.  But maybe we need to
filter it above.

> > @@ -199,9 +202,17 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
> >  			}
> >  		}
> >  populate:
> > +		pageshift = PAGE_SHIFT;
> > +		if (PageCompound(page))
> > +			pageshift += compound_order(compound_head(page));
> > +		mem->pageshift = min(mem->pageshift, pageshift);
> >  		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
> >  	}
> >  
> > +	/* We have an incomplete huge page, default to PAGE_SHIFT */
> > +	if (head)
> > +		mem->pageshift = PAGE_SHIFT;
> > +
> 
> You never set head AFIACS? (other than in the initialiser)

That looks like a leftover from the previous version.

> 
> cheers
>

Patch

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 896efa5..79d570c 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -35,9 +35,9 @@  extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(
 extern struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
 		unsigned long ua, unsigned long entries);
 extern long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa);
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa);
 extern long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa);
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa);
 extern long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem);
 extern void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem);
 #endif
diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index d066e37..8c456fa 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -449,7 +449,7 @@  long kvmppc_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
 		/* This only handles v2 IOMMU type, v1 is handled via ioctl() */
 		return H_TOO_HARD;
 
-	if (WARN_ON_ONCE(mm_iommu_ua_to_hpa(mem, ua, &hpa)))
+	if (WARN_ON_ONCE(mm_iommu_ua_to_hpa(mem, ua, tbl->it_page_shift, &hpa)))
 		return H_HARDWARE;
 
 	if (mm_iommu_mapped_inc(mem))
diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
index 925fc31..5b298f5 100644
--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
@@ -279,7 +279,8 @@  static long kvmppc_rm_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
 	if (!mem)
 		return H_TOO_HARD;
 
-	if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, &hpa)))
+	if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, tbl->it_page_shift,
+			&hpa)))
 		return H_HARDWARE;
 
 	pua = (void *) vmalloc_to_phys(pua);
@@ -469,7 +470,8 @@  long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
 
 		mem = mm_iommu_lookup_rm(vcpu->kvm->mm, ua, IOMMU_PAGE_SIZE_4K);
 		if (mem)
-			prereg = mm_iommu_ua_to_hpa_rm(mem, ua, &tces) == 0;
+			prereg = mm_iommu_ua_to_hpa_rm(mem, ua,
+					IOMMU_PAGE_SHIFT_4K, &tces) == 0;
 	}
 
 	if (!prereg) {
diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index abb4364..11e1029 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -27,6 +27,7 @@  struct mm_iommu_table_group_mem_t {
 	struct rcu_head rcu;
 	unsigned long used;
 	atomic64_t mapped;
+	unsigned int pageshift;
 	u64 ua;			/* userspace address */
 	u64 entries;		/* number of entries in hpas[] */
 	u64 *hpas;		/* vmalloc'ed */
@@ -125,7 +126,8 @@  long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 {
 	struct mm_iommu_table_group_mem_t *mem;
 	long i, j, ret = 0, locked_entries = 0;
-	struct page *page = NULL;
+	unsigned int pageshift;
+	struct page *page = NULL, *head = NULL;
 
 	mutex_lock(&mem_list_mutex);
 
@@ -159,6 +161,7 @@  long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	mem->pageshift = __builtin_ctzl(ua | (entries << PAGE_SHIFT));
 	mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0])));
 	if (!mem->hpas) {
 		kfree(mem);
@@ -199,9 +202,17 @@  long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min(mem->pageshift, pageshift);
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
 
+	/* We have an incomplete huge page, default to PAGE_SHIFT */
+	if (head)
+		mem->pageshift = PAGE_SHIFT;
+
 	atomic64_set(&mem->mapped, 1);
 	mem->used = 1;
 	mem->ua = ua;
@@ -349,7 +360,7 @@  struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
 EXPORT_SYMBOL_GPL(mm_iommu_find);
 
 long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	u64 *va = &mem->hpas[entry];
@@ -357,6 +368,9 @@  long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	*hpa = *va | (ua & ~PAGE_MASK);
 
 	return 0;
@@ -364,7 +378,7 @@  long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
 
 long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	void *va = &mem->hpas[entry];
@@ -373,6 +387,9 @@  long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	pa = (void *) vmalloc_to_phys(va);
 	if (!pa)
 		return -EFAULT;
diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 2da5f05..7cd63b0 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -467,7 +467,7 @@  static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
 	if (!mem)
 		return -EINVAL;
 
-	ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
+	ret = mm_iommu_ua_to_hpa(mem, tce, shift, phpa);
 	if (ret)
 		return -EINVAL;