On Sat, 7 Jul 2018 20:44:10 +1000 Alexey Kardashevskiy <a...@ozlabs.ru> 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 hugepagetlb's compound page size. > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > --- > 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(). > @@ -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. > @@ -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. > + 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
