On Wed, Jan 20, 2021 at 08:06:07PM +0200, Mike Rapoport wrote:

+static struct page *secretmem_alloc_page(gfp_t gfp)
+{
+	/*
+	 * FIXME: use a cache of large pages to reduce the direct map
+	 * fragmentation
+	 */
+	return alloc_page(gfp);
+}
+
+static vm_fault_t secretmem_fault(struct vm_fault *vmf)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	pgoff_t offset = vmf->pgoff;
+	unsigned long addr;
+	struct page *page;
+	int err;
+
+	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
+		return vmf_error(-EINVAL);
+
+retry:
+	page = find_lock_page(mapping, offset);
+	if (!page) {
+		page = secretmem_alloc_page(vmf->gfp_mask);
+		if (!page)
+			return VM_FAULT_OOM;
+
+		err = set_direct_map_invalid_noflush(page, 1);
+		if (err)
+			return vmf_error(err);

Haven't we leaked the page at this point?

+		__SetPageUptodate(page);
+		err = add_to_page_cache(page, mapping, offset, vmf->gfp_mask);

At this point, doesn't the page contain data from the last person to use
the page?  ie we've leaked data to this process?  I don't see anywhere
that we write data to the page.


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