On Tue, Jul 17, 2018 at 05:19:13PM +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. For the page shift this uses the shift > returned by find_linux_pte() which indicates how the page is mapped to > the current userspace - if the page is huge and this is not a zero, then > it is a leaf pte and the page is mapped within the range. > > Signed-off-by: Alexey Kardashevskiy Reviewed-by: David Gibson > --- > > v6 got a couple of rb's but since the patch has changed again, I am not > putting them here yet. > > Reviewed-by: David Gibson > Reviewed-by: Nicholas Piggin > > --- > Changes: > v7: > * do not fail if pte is not found, fall back to the default case instead > > v6: > * replaced hugetlbfs with pageshift from find_linux_pte() > > 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 | 37 ++++++++++++++++++++++++++++++++-- > drivers/vfio/vfio_iommu_spapr_tce.c | 2 +- > 5 files changed, 43 insertions(+), 8 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..a4ca576 100644 > --- a/arch/powerpc/mm/mmu_context_iommu.c > +++ b/arch/powerpc/mm/mmu_context_iommu.c > @@ -19,6 +19,7 @@ > #include > #include > #include > +#include > > 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 +127,8 @@ 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; > + unsigned int pageshift; > + unsigned long flags; > struct page *page = NULL; > > mutex_lock(&mem_list_mutex); > @@ -159,6 +163,12 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries, > goto unlock_exit; > } > > + /* > + * For a starting point for a maximum page size calculation > + * we use @ua and @entries natural alignment to allow IOMMU pages > + * smaller than huge pages but still bigger than PAGE_SIZE. > + */ > + mem->pageshift = __ffs(ua | (entries << PAGE_SHIFT)); > mem->hpas = vzalloc(array_size(entries, sizeof(mem->hpas[0]))); > if (!mem->hpas) { > kfree(mem); > @@ -199,6 +209,23 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries, > } > } > populate: > + pageshift = PAGE_SHIFT; > + if (PageCompound(page)) { > + pte_t *pte; > + struct page *head = compound_head(page); > + unsigned int compshift = compound_order(head); > + > + local_irq_save(flags); /* disables as well */ > + pte = find_linux_pte(mm->pgd, ua, NULL, &pageshift); > + local_irq_restore(flags); > + > + /* Double check it is still the same pinned page */ > + if (pte && pte_page(*pte) == head && > + pageshift == compshift) > + pageshift = max_t(unsigned int, pageshift, > + PAGE_SHIFT); > + } > + mem->pageshift = min(mem->pageshift, pageshift); > mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT; > } > > @@ -349,7 +376,7 @@ 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 +384,9 @@ 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 +394,7 @@ 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 +403,9 @@ 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; > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson