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    SubjectRe: [PATCH v3 08/16] s390/pci: Remove races against pte updates
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    On 10/21/20 10:56 AM, Daniel Vetter wrote:
    > Way back it was a reasonable assumptions that iomem mappings never
    > change the pfn range they point at. But this has changed:
    >
    > - gpu drivers dynamically manage their memory nowadays, invalidating
    > ptes with unmap_mapping_range when buffers get moved
    >
    > - contiguous dma allocations have moved from dedicated carvetouts to
    > cma regions. This means if we miss the unmap the pfn might contain
    > pagecache or anon memory (well anything allocated with GFP_MOVEABLE)
    >
    > - even /dev/mem now invalidates mappings when the kernel requests that
    > iomem region when CONFIG_IO_STRICT_DEVMEM is set, see commit
    > 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the
    > region")
    >
    > Accessing pfns obtained from ptes without holding all the locks is
    > therefore no longer a good idea. Fix this.
    >
    > Since zpci_memcpy_from|toio seems to not do anything nefarious with
    > locks we just need to open code get_pfn and follow_pfn and make sure
    > we drop the locks only after we're done. The write function also needs
    > the copy_from_user move, since we can't take userspace faults while
    > holding the mmap sem.
    >
    > v2: Move VM_IO | VM_PFNMAP checks around so they keep returning EINVAL
    > like before (Gerard)
    >
    > v3: Polish commit message (Niklas)
    >
    > Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
    > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
    > Cc: Jason Gunthorpe <jgg@ziepe.ca>
    > Cc: Dan Williams <dan.j.williams@intel.com>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: John Hubbard <jhubbard@nvidia.com>
    > Cc: Jérôme Glisse <jglisse@redhat.com>
    > Cc: Jan Kara <jack@suse.cz>
    > Cc: linux-mm@kvack.org
    > Cc: linux-arm-kernel@lists.infradead.org
    > Cc: linux-samsung-soc@vger.kernel.org
    > Cc: linux-media@vger.kernel.org
    > Cc: Niklas Schnelle <schnelle@linux.ibm.com>
    > Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
    > Cc: linux-s390@vger.kernel.org
    > Cc: Niklas Schnelle <schnelle@linux.ibm.com>
    > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.com>
    ^^^^
    This should be ".ch", but since this is clearly a typo and you also send from @ffwll.ch,
    I took the liberty and fixed it for this commit and applied your patch to our internal
    branch, Heiko or Vasily will then pick it up for the s390 tree.

    Thanks!

    > ---
    > arch/s390/pci/pci_mmio.c | 98 +++++++++++++++++++++++-----------------
    > 1 file changed, 57 insertions(+), 41 deletions(-)
    >
    > diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c
    > index 401cf670a243..1a6adbc68ee8 100644
    > --- a/arch/s390/pci/pci_mmio.c
    > +++ b/arch/s390/pci/pci_mmio.c
    > @@ -119,33 +119,15 @@ static inline int __memcpy_toio_inuser(void __iomem *dst,
    > return rc;
    > }
    >
    > -static long get_pfn(unsigned long user_addr, unsigned long access,
    > - unsigned long *pfn)
    > -{
    > - struct vm_area_struct *vma;
    > - long ret;
    > -
    > - mmap_read_lock(current->mm);
    > - ret = -EINVAL;
    > - vma = find_vma(current->mm, user_addr);
    > - if (!vma)
    > - goto out;
    > - ret = -EACCES;
    > - if (!(vma->vm_flags & access))
    > - goto out;
    > - ret = follow_pfn(vma, user_addr, pfn);
    > -out:
    > - mmap_read_unlock(current->mm);
    > - return ret;
    > -}
    > -
    > SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
    > const void __user *, user_buffer, size_t, length)
    > {
    > u8 local_buf[64];
    > void __iomem *io_addr;
    > void *buf;
    > - unsigned long pfn;
    > + struct vm_area_struct *vma;
    > + pte_t *ptep;
    > + spinlock_t *ptl;
    > long ret;
    >
    > if (!zpci_is_enabled())
    > @@ -158,7 +140,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
    > * We only support write access to MIO capable devices if we are on
    > * a MIO enabled system. Otherwise we would have to check for every
    > * address if it is a special ZPCI_ADDR and would have to do
    > - * a get_pfn() which we don't need for MIO capable devices. Currently
    > + * a pfn lookup which we don't need for MIO capable devices. Currently
    > * ISM devices are the only devices without MIO support and there is no
    > * known need for accessing these from userspace.
    > */
    > @@ -176,21 +158,37 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
    > } else
    > buf = local_buf;
    >
    > - ret = get_pfn(mmio_addr, VM_WRITE, &pfn);
    > + ret = -EFAULT;
    > + if (copy_from_user(buf, user_buffer, length))
    > + goto out_free;
    > +
    > + mmap_read_lock(current->mm);
    > + ret = -EINVAL;
    > + vma = find_vma(current->mm, mmio_addr);
    > + if (!vma)
    > + goto out_unlock_mmap;
    > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
    > + goto out_unlock_mmap;
    > + ret = -EACCES;
    > + if (!(vma->vm_flags & VM_WRITE))
    > + goto out_unlock_mmap;
    > +
    > + ret = follow_pte_pmd(vma->vm_mm, mmio_addr, NULL, &ptep, NULL, &ptl);
    > if (ret)
    > - goto out;
    > - io_addr = (void __iomem *)((pfn << PAGE_SHIFT) |
    > + goto out_unlock_mmap;
    > +
    > + io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) |
    > (mmio_addr & ~PAGE_MASK));
    >
    > - ret = -EFAULT;
    > if ((unsigned long) io_addr < ZPCI_IOMAP_ADDR_BASE)
    > - goto out;
    > -
    > - if (copy_from_user(buf, user_buffer, length))
    > - goto out;
    > + goto out_unlock_pt;
    >
    > ret = zpci_memcpy_toio(io_addr, buf, length);
    > -out:
    > +out_unlock_pt:
    > + pte_unmap_unlock(ptep, ptl);
    > +out_unlock_mmap:
    > + mmap_read_unlock(current->mm);
    > +out_free:
    > if (buf != local_buf)
    > kfree(buf);
    > return ret;
    > @@ -274,7 +272,9 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
    > u8 local_buf[64];
    > void __iomem *io_addr;
    > void *buf;
    > - unsigned long pfn;
    > + struct vm_area_struct *vma;
    > + pte_t *ptep;
    > + spinlock_t *ptl;
    > long ret;
    >
    > if (!zpci_is_enabled())
    > @@ -287,7 +287,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
    > * We only support read access to MIO capable devices if we are on
    > * a MIO enabled system. Otherwise we would have to check for every
    > * address if it is a special ZPCI_ADDR and would have to do
    > - * a get_pfn() which we don't need for MIO capable devices. Currently
    > + * a pfn lookup which we don't need for MIO capable devices. Currently
    > * ISM devices are the only devices without MIO support and there is no
    > * known need for accessing these from userspace.
    > */
    > @@ -306,22 +306,38 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
    > buf = local_buf;
    > }
    >
    > - ret = get_pfn(mmio_addr, VM_READ, &pfn);
    > + mmap_read_lock(current->mm);
    > + ret = -EINVAL;
    > + vma = find_vma(current->mm, mmio_addr);
    > + if (!vma)
    > + goto out_unlock_mmap;
    > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
    > + goto out_unlock_mmap;
    > + ret = -EACCES;
    > + if (!(vma->vm_flags & VM_WRITE))
    > + goto out_unlock_mmap;
    > +
    > + ret = follow_pte_pmd(vma->vm_mm, mmio_addr, NULL, &ptep, NULL, &ptl);
    > if (ret)
    > - goto out;
    > - io_addr = (void __iomem *)((pfn << PAGE_SHIFT) | (mmio_addr & ~PAGE_MASK));
    > + goto out_unlock_mmap;
    > +
    > + io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) |
    > + (mmio_addr & ~PAGE_MASK));
    >
    > if ((unsigned long) io_addr < ZPCI_IOMAP_ADDR_BASE) {
    > ret = -EFAULT;
    > - goto out;
    > + goto out_unlock_pt;
    > }
    > ret = zpci_memcpy_fromio(buf, io_addr, length);
    > - if (ret)
    > - goto out;
    > - if (copy_to_user(user_buffer, buf, length))
    > +
    > +out_unlock_pt:
    > + pte_unmap_unlock(ptep, ptl);
    > +out_unlock_mmap:
    > + mmap_read_unlock(current->mm);
    > +
    > + if (!ret && copy_to_user(user_buffer, buf, length))
    > ret = -EFAULT;
    >
    > -out:
    > if (buf != local_buf)
    > kfree(buf);
    > return ret;
    >

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