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Subject[PATCH 3/7] dax: Check the end of the block-device capacity with dax_direct_access()
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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.

Cc: Jan Kara <jack@suse.cz>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/super.c | 39 +++++++++++++++++++++++++++++----------
1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 6e928f37d084..a27395cfcec6 100644
--- 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 +115,15 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
return false;
}

+ last_page = ALIGN_DOWN(part_nr_sects_read(bdev->bd_part)
+ - PAGE_SIZE / 512, PAGE_SIZE / 512);
+ 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 +132,15 @@ 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 +155,20 @@ 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) {
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