[PATCH kernel v5 2/2] KVM: PPC: Check if IOMMU page is contained in the pinned physical page
Nicholas Piggin
npiggin at gmail.com
Sat Jul 7 23:47:42 AEST 2018
On Sat, 7 Jul 2018 22:44:45 +1000
Alexey Kardashevskiy <aik at ozlabs.ru> wrote:
> On Sat, 7 Jul 2018 21:43:03 +1000
> Nicholas Piggin <npiggin at gmail.com> wrote:
>
> > On Sat, 7 Jul 2018 20:44:10 +1000
> > Alexey Kardashevskiy <aik at 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 <aik at 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 at 800000020000000/ethernet at 0
> > > mlx5_core 0000:00:00.0: failed to map direct window for /pci at 800000020000000/ethernet at 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?
> >
> > > @@ -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
More information about the Linuxppc-dev
mailing list