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

[Jan Kara <jack@suse.cz>]

On Tue 12-02-19 13:24:56, Dan Williams wrote:
> 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);

Why not just (i_size_read(bdev->bd_inode) - 1) >> PAGE_SHIFT? Otherwise the
patch looks good to me.

								Honza


> +	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) {
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR