dax: Check the end of the block-device capacity with dax_direct_access()

The checks in __bdev_dax_supported() helped mitigate a potential data
corruption bug in the pmem driver's handling of section alignment
padding. Strengthen the checks, including checking the end of the range,
to validate the dev_pagemap, Xarray entries, and sector-to-pfn
translation established for pmem namespaces.

Acked-by: Jan Kara <jack@suse.cz>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 6e928f3..0cb8c30 100644 (file)
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -86,12 +86,14 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
 {
        struct dax_device *dax_dev;
        bool dax_enabled = false;
+       pgoff_t pgoff, pgoff_end;
        struct request_queue *q;
-       pgoff_t pgoff;
-       int err, id;
-       pfn_t pfn;
-       long len;
        char buf[BDEVNAME_SIZE];
+       void *kaddr, *end_kaddr;
+       pfn_t pfn, end_pfn;
+       sector_t last_page;
+       long len, len2;
+       int err, id;
 
        if (blocksize != PAGE_SIZE) {
                pr_debug("%s: error: unsupported blocksize for dax\n",
@@ -113,6 +115,14 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
                return false;
        }
 
+       last_page = PFN_DOWN(i_size_read(bdev->bd_inode) - 1) * 8;
+       err = bdev_dax_pgoff(bdev, last_page, PAGE_SIZE, &pgoff_end);
+       if (err) {
+               pr_debug("%s: error: unaligned partition for dax\n",
+                               bdevname(bdev, buf));
+               return false;
+       }
+
        dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
        if (!dax_dev) {
                pr_debug("%s: error: device does not support dax\n",
@@ -121,14 +131,15 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
        }
 
        id = dax_read_lock();
-       len = dax_direct_access(dax_dev, pgoff, 1, NULL, &pfn);
+       len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
+       len2 = dax_direct_access(dax_dev, pgoff_end, 1, &end_kaddr, &end_pfn);
        dax_read_unlock(id);
 
        put_dax(dax_dev);
 
-       if (len < 1) {
+       if (len < 1 || len2 < 1) {
                pr_debug("%s: error: dax access failed (%ld)\n",
-                               bdevname(bdev, buf), len);
+                               bdevname(bdev, buf), len < 1 ? len : len2);
                return false;
        }
 
@@ -143,13 +154,20 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
                 */
                WARN_ON(IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API));
                dax_enabled = true;
-       } else if (pfn_t_devmap(pfn)) {
-               struct dev_pagemap *pgmap;
+       } else if (pfn_t_devmap(pfn) && pfn_t_devmap(end_pfn)) {
+               struct dev_pagemap *pgmap, *end_pgmap;
 
                pgmap = get_dev_pagemap(pfn_t_to_pfn(pfn), NULL);
-               if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)
+               end_pgmap = get_dev_pagemap(pfn_t_to_pfn(end_pfn), NULL);
+               if (pgmap && pgmap == end_pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX
+                               && pfn_t_to_page(pfn)->pgmap == pgmap
+                               && pfn_t_to_page(end_pfn)->pgmap == pgmap
+                               && pfn_t_to_pfn(pfn) == PHYS_PFN(__pa(kaddr))
+                               && pfn_t_to_pfn(end_pfn) == PHYS_PFN(__pa(end_kaddr)))
                        dax_enabled = true;
                put_dev_pagemap(pgmap);
+               put_dev_pagemap(end_pgmap);
+
        }
 
        if (!dax_enabled) {