[PATCH kernel v5 0/2] KVM: PPC: Check if IOMMU page is contained in the pinned physical page

This is to improve page boundaries checking and should probably
be cc:stable. I came accross this while debugging nvlink2 passthrough
but the lack of checking might be exploited by the existing userspace.

The get_user_pages() comment says it should be "phased out" but the only
alternative seems to be get_user_pages_longterm(), should that be used
instead (this is longterm reference elevation, however it is not DAX,
whatever this implies)? get_user_pages_remote() seems unnecessarily
complicated because of @locked.


Changes:
v5:
* 2/2: changed compound pages handling

v4:
* 2/2: implemented less strict but still safe max pageshift as David suggested

v3:
* enforced huge pages not to cross preregistered chunk boundaries

v2:
* 2/2: explicitly check for compound pages before calling compound_order()



This is based on sha1
021c917 Linus Torvalds "Linux 4.18-rc3".

Please comment. Thanks.



Alexey Kardashevskiy (2):
  vfio/spapr: Use IOMMU pageshift rather than pagesize
  KVM: PPC: Check if IOMMU page is contained in the pinned physical page

 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    | 33 +++++++++++++++++++++++++++------
 drivers/vfio/vfio_iommu_spapr_tce.c    | 10 +++++-----
 5 files changed, 39 insertions(+), 16 deletions(-)

-- 
2.11.0

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 hugepagetlb's compound page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v5:
* only consider compound pages from hugetlbfs

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    | 33 +++++++++++++++++++++++++++------
 drivers/vfio/vfio_iommu_spapr_tce.c    |  2 +-
 5 files changed, 35 insertions(+), 12 deletions(-)

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..0aebed6 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c

@@ -18,6 +18,7 @@
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
 #include <linux/swap.h>
+#include <linux/hugetlb.h>
 #include <asm/mmu_context.h>
 
 static DEFINE_MUTEX(mem_list_mutex);

@@ -27,6 +28,7 @@ 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 */

@@ -125,6 +127,7 @@ 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;
+	unsigned int pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -159,6 +162,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	/*
+	 * Use @ua and @entries alignment as a starting point for a maximum
+	 * page size calculation below.
+	 */
+	mem->pageshift = __ffs(ua | (entries << PAGE_SHIFT));
 	mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0])));
 	if (!mem->hpas) {
 		kfree(mem);

@@ -167,8 +175,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 	}
 
 	for (i = 0; i < entries; ++i) {
-		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
-					1/* pages */, 1/* iswrite */, &page)) {
+		struct vm_area_struct *vma = NULL;
+
+		if (1 != get_user_pages(ua + (i << PAGE_SHIFT),
+					1/* pages */, 1/* iswrite */, &page,
+					&vma)) {
 			ret = -EFAULT;
 			for (j = 0; j < i; ++j)
 				put_page(pfn_to_page(mem->hpas[j] >>

@@ -186,9 +197,9 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		if (is_migrate_cma_page(page)) {
 			if (mm_iommu_move_page_from_cma(page))
 				goto populate;
-			if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
+			if (1 != get_user_pages(ua + (i << PAGE_SHIFT),
 						1/* pages */, 1/* iswrite */,
-						&page)) {
+						&page, &vma)) {
 				ret = -EFAULT;
 				for (j = 0; j < i; ++j)
 					put_page(pfn_to_page(mem->hpas[j] >>

@@ -199,6 +210,10 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (vma && vma->vm_file && is_file_hugepages(vma->vm_file))
+			pageshift += hstate_vma(vma)->order;
+		mem->pageshift = min(mem->pageshift, pageshift);
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
 

@@ -349,7 +364,7 @@ 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 +372,9 @@ 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 +382,7 @@ 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 +391,9 @@ 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;
 

-- 
2.11.0

The size is always equal to 1 page so let's use this. Later on this will
be used for other checks which use page shifts to check the granularity
of access.

This should cause no behavioral change.

Reviewed-by: David Gibson <redacted>
Acked-by: Alex Williamson <redacted>
Signed-off-by: Alexey Kardashevskiy <redacted>
---

As Alex suggested, this should go via the ppc tree which the next patch
is going to (which is ppc-kvm).
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 759a5bd..2da5f05 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c

@@ -457,13 +457,13 @@ static void tce_iommu_unuse_page(struct tce_container *container,
 }
 
 static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
-		unsigned long tce, unsigned long size,
+		unsigned long tce, unsigned long shift,
 		unsigned long *phpa, struct mm_iommu_table_group_mem_t **pmem)
 {
 	long ret = 0;
 	struct mm_iommu_table_group_mem_t *mem;
 
-	mem = mm_iommu_lookup(container->mm, tce, size);
+	mem = mm_iommu_lookup(container->mm, tce, 1ULL << shift);
 	if (!mem)
 		return -EINVAL;
 

@@ -487,7 +487,7 @@ static void tce_iommu_unuse_page_v2(struct tce_container *container,
 	if (!pua)
 		return;
 
-	ret = tce_iommu_prereg_ua_to_hpa(container, *pua, IOMMU_PAGE_SIZE(tbl),
+	ret = tce_iommu_prereg_ua_to_hpa(container, *pua, tbl->it_page_shift,
 			&hpa, &mem);
 	if (ret)
 		pr_debug("%s: tce %lx at #%lx was not cached, ret=%d\n",

@@ -611,7 +611,7 @@ static long tce_iommu_build_v2(struct tce_container *container,
 				entry + i);
 
 		ret = tce_iommu_prereg_ua_to_hpa(container,
-				tce, IOMMU_PAGE_SIZE(tbl), &hpa, &mem);
+				tce, tbl->it_page_shift, &hpa, &mem);
 		if (ret)
 			break;
 

-- 
2.11.0

On Sat,  7 Jul 2018 20:44:10 +1000
Alexey Kardashevskiy [off-list ref] wrote:

I think it would be better to start with UINT_MAX or something to make
it clear that it's not a valid "guess" but rather just a starting point
for the min().

You need mmap_sem for read here, and held while you inspect the vma.
I would say don't hold it over the error handling and the
mm_iommu_move_page_from_cma() call though.

I would just set to huge_page_shift() here so you don't expose this
hstate quirk that adds order to PAGE_SIZE.

+		mem->pageshift = min(mem->pageshift, pageshift);
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
 

Otherwise the mm side of things looks okay, I think.

Thanks,
Nick

On Sat, 7 Jul 2018 21:43:03 +1000
Nicholas Piggin [off-list ref] wrote:

On Sat,  7 Jul 2018 20:44:10 +1000
Alexey Kardashevskiy [off-list ref] wrote:

quoted

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 hugepagetlb's compound page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v5:
* only consider compound pages from hugetlbfs

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    | 33 +++++++++++++++++++++++++++------
 drivers/vfio/vfio_iommu_spapr_tce.c    |  2 +-
 5 files changed, 35 insertions(+), 12 deletions(-)

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..0aebed6 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c

@@ -18,6 +18,7 @@
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
 #include <linux/swap.h>
+#include <linux/hugetlb.h>
 #include <asm/mmu_context.h>
 
 static DEFINE_MUTEX(mem_list_mutex);

@@ -27,6 +28,7 @@ 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 */

@@ -125,6 +127,7 @@ 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;
+	unsigned int pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -159,6 +162,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	/*
+	 * Use @ua and @entries alignment as a starting point for a maximum
+	 * page size calculation below.
+	 */
+	mem->pageshift = __ffs(ua | (entries << PAGE_SHIFT));
 	mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0])));
 	if (!mem->hpas) {
 		kfree(mem);  

I think it would be better to start with UINT_MAX or something to make
it clear that it's not a valid "guess" but rather just a starting point
for the min().

This is to handle unaligned @ua/@entries backed by a huge page. For
example, 1GB page and we are preregistering only a second half of it -
the maximum pageshift should be 29 instead of 30 which it will be if we
start from 64.

quoted

@@ -167,8 +175,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 	}
 
 	for (i = 0; i < entries; ++i) {
-		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
-					1/* pages */, 1/* iswrite */, &page)) {
+		struct vm_area_struct *vma = NULL;
+
+		if (1 != get_user_pages(ua + (i << PAGE_SHIFT),
+					1/* pages */, 1/* iswrite */, &page,
+					&vma)) {
 			ret = -EFAULT;
 			for (j = 0; j < i; ++j)
 				put_page(pfn_to_page(mem->hpas[j] >>  

You need mmap_sem for read here, and held while you inspect the vma.
I would say don't hold it over the error handling and the
mm_iommu_move_page_from_cma() call though.

Ah, this is why it deadlocked when I tried this.

But do I really need mmap_sem here? get_user_pages_longterm() inspects
vma with no mmap_sem held in case of VFIO IOMMU Type1:

vfio_fops_unl_ioctl
  vfio_iommu_type1_ioctl
    vfio_dma_do_map
      vfio_pin_map_dma
        vfio_pin_pages_remote
          vaddr_get_pfn
            get_user_pages_longterm

Is that a bug? Other cases seem to hold it though.

quoted

@@ -186,9 +197,9 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		if (is_migrate_cma_page(page)) {
 			if (mm_iommu_move_page_from_cma(page))
 				goto populate;
-			if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
+			if (1 != get_user_pages(ua + (i << PAGE_SHIFT),
 						1/* pages */, 1/* iswrite */,
-						&page)) {
+						&page, &vma)) {
 				ret = -EFAULT;
 				for (j = 0; j < i; ++j)
 					put_page(pfn_to_page(mem->hpas[j] >>

@@ -199,6 +210,10 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (vma && vma->vm_file && is_file_hugepages(vma->vm_file))
+			pageshift += hstate_vma(vma)->order;  

I would just set to huge_page_shift() here so you don't expose this
hstate quirk that adds order to PAGE_SIZE.

Ah, right, there is a million helpers for this :)

 

quoted

+		mem->pageshift = min(mem->pageshift, pageshift);
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
   

Otherwise the mm side of things looks okay, I think.

Thanks for the review.

--
Alexey

On Sat, 7 Jul 2018 22:44:45 +1000
Alexey Kardashevskiy [off-list ref] wrote:

On Sat, 7 Jul 2018 21:43:03 +1000
Nicholas Piggin [off-list ref] wrote:

quoted

On Sat,  7 Jul 2018 20:44:10 +1000
Alexey Kardashevskiy [off-list ref] wrote:
  

quoted

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 hugepagetlb's compound page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v5:
* only consider compound pages from hugetlbfs

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    | 33 +++++++++++++++++++++++++++------
 drivers/vfio/vfio_iommu_spapr_tce.c    |  2 +-
 5 files changed, 35 insertions(+), 12 deletions(-)

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..0aebed6 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c

@@ -18,6 +18,7 @@
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
 #include <linux/swap.h>
+#include <linux/hugetlb.h>
 #include <asm/mmu_context.h>
 
 static DEFINE_MUTEX(mem_list_mutex);

@@ -27,6 +28,7 @@ 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 */

@@ -125,6 +127,7 @@ 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;
+	unsigned int pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -159,6 +162,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	/*
+	 * Use @ua and @entries alignment as a starting point for a maximum
+	 * page size calculation below.
+	 */
+	mem->pageshift = __ffs(ua | (entries << PAGE_SHIFT));
 	mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0])));
 	if (!mem->hpas) {
 		kfree(mem);    

I think it would be better to start with UINT_MAX or something to make
it clear that it's not a valid "guess" but rather just a starting point
for the min().  

This is to handle unaligned @ua/@entries backed by a huge page. For
example, 1GB page and we are preregistering only a second half of it -
the maximum pageshift should be 29 instead of 30 which it will be if we
start from 64.

Ah okay that's what I'm missing. Maybe a small addition to the comment?

quoted

quoted

@@ -167,8 +175,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 	}
 
 	for (i = 0; i < entries; ++i) {
-		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
-					1/* pages */, 1/* iswrite */, &page)) {
+		struct vm_area_struct *vma = NULL;
+
+		if (1 != get_user_pages(ua + (i << PAGE_SHIFT),
+					1/* pages */, 1/* iswrite */, &page,
+					&vma)) {
 			ret = -EFAULT;
 			for (j = 0; j < i; ++j)
 				put_page(pfn_to_page(mem->hpas[j] >>    

You need mmap_sem for read here, and held while you inspect the vma.
I would say don't hold it over the error handling and the
mm_iommu_move_page_from_cma() call though.  

Ah, this is why it deadlocked when I tried this.

But do I really need mmap_sem here? get_user_pages_longterm() inspects
vma with no mmap_sem held in case of VFIO IOMMU Type1:

vfio_fops_unl_ioctl
  vfio_iommu_type1_ioctl
    vfio_dma_do_map
      vfio_pin_map_dma
        vfio_pin_pages_remote
          vaddr_get_pfn
            get_user_pages_longterm

Is that a bug? Other cases seem to hold it though.

Yes you need mmap_sem. I think that would be a bug too.

Thanks,
Nick