Re: [PATCH v4 14/23] iommufd: Add mmap interface

Jason Gunthorpe
2025-05-15T16:47:21Z

On Thu, May 08, 2025 at 08:02:35PM -0700, Nicolin Chen wrote:
> +int _iommufd_alloc_mmap(struct iommufd_ctx *ictx, struct iommufd_object *owner,
> + phys_addr_t base, size_t length, unsigned long *offset)
> +{
> + struct iommufd_mmap *immap;
> + unsigned long startp;
> + int num_pfns, rc;
> +
> + if (WARN_ON_ONCE(!offset))
> + return -EINVAL;

We don't need checks like this, just let it oops

> + if (!PAGE_ALIGNED(base))
> + return -EINVAL;
> + if (!length || !PAGE_ALIGNED(length))
> + return -EINVAL;
> + num_pfns = length >> PAGE_SHIFT;
> +
> + immap = kzalloc(sizeof(*immap), GFP_KERNEL);
> + if (!immap)
> + return -ENOMEM;
> + immap->owner = owner;
> + immap->base_pfn = base >> PAGE_SHIFT;

'base' is a confusing name for the mmio address. Call it mmio_pfn or something

> +static int iommufd_fops_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> + struct iommufd_ctx *ictx = filp->private_data;
> + size_t length = vma->vm_end - vma->vm_start;
> + struct iommufd_mmap *immap;
> + int rc;
> +
> + if (!PAGE_ALIGNED(length))
> + return -EINVAL;
> + if (!(vma->vm_flags & VM_SHARED))
> + return -EINVAL;
> + if (vma->vm_flags & VM_EXEC)
> + return -EPERM;
> +
> + /* vma->vm_pgoff carries an index to an mtree entry (immap) */
> + immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
> + if (!immap)
> + return -ENXIO;
> + if (length >> PAGE_SHIFT != immap->num_pfns)
> + return -ENXIO;

This needs to validate that vm_pgoff is at the start of the immap or
num_pfns is the wrong thing to validate length against.

length >> PAGE_SHIFT will truncate non-zero bits which will not check
it properly.

> + vma->vm_pgoff = 0;
> + vma->vm_private_data = immap;
> + vma->vm_ops = &iommufd_vma_ops;
> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> + vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO);

remap_pfn_range already sets these vm_flags

> + rc = remap_pfn_range(vma, vma->vm_start, immap->base_pfn, length,
> + vma->vm_page_prot);

This shoudl be io_remap_pfn_range() if it is mmio

> + if (!rc) /* vm_ops.open won't be called for mmap itself. */
> + refcount_inc(&immap->owner->users);
> + return rc;

Success oriented flow

Jason