Re: [PATCH v10 12/13] libnvdimm/pfn: Fix fsdax-mode namespace info-block zero-fields

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Dan Williams <dan.j.williams@intel.com>, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, linux-nvdimm@lists.01.org
Subject: Re: [PATCH v10 12/13] libnvdimm/pfn: Fix fsdax-mode namespace info-block zero-fields
Date: Wed, 19 Jun 2019 22:00:18 +0530	[thread overview]
Message-ID: <877e9hk06d.fsf@linux.ibm.com> (raw)
In-Reply-To: <156092356065.979959.6681003754765958296.stgit@dwillia2-desk3.amr.corp.intel.com>

Dan Williams <dan.j.williams@intel.com> writes:

> At namespace creation time there is the potential for the "expected to
> be zero" fields of a 'pfn' info-block to be filled with indeterminate
> data. While the kernel buffer is zeroed on allocation it is immediately
> overwritten by nd_pfn_validate() filling it with the current contents of
> the on-media info-block location. For fields like, 'flags' and the
> 'padding' it potentially means that future implementations can not rely
> on those fields being zero.
>
> In preparation to stop using the 'start_pad' and 'end_trunc' fields for
> section alignment, arrange for fields that are not explicitly
> initialized to be guaranteed zero. Bump the minor version to indicate it
> is safe to assume the 'padding' and 'flags' are zero. Otherwise, this
> corruption is expected to benign since all other critical fields are
> explicitly initialized.
>
> Note The cc: stable is about spreading this new policy to as many
> kernels as possible not fixing an issue in those kernels. It is not
> until the change titled "libnvdimm/pfn: Stop padding pmem namespaces to
> section alignment" where this improper initialization becomes a problem.
> So if someone decides to backport "libnvdimm/pfn: Stop padding pmem
> namespaces to section alignment" (which is not tagged for stable), make
> sure this pre-requisite is flagged.

Don't we need a change like below in this patch?

modified   drivers/nvdimm/pfn_devs.c
@@ -452,10 +452,11 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
 	if (memcmp(pfn_sb->parent_uuid, parent_uuid, 16) != 0)
 		return -ENODEV;
 
-	if (__le16_to_cpu(pfn_sb->version_minor) < 1) {
-		pfn_sb->start_pad = 0;
-		pfn_sb->end_trunc = 0;
-	}
+	if ((__le16_to_cpu(pfn_sb->version_minor) < 1) ||
+	    (__le16_to_cpu(pfn_sb->version_minor) >= 3)) {
+			pfn_sb->start_pad = 0;
+			pfn_sb->end_trunc = 0;
+		}


IIUC we want to force the start_pad and end_truc to zero if the pfn_sb
minor version number >= 3. So once we have this patch backported and
older kernel finds a pfn_sb with minor version 3, it will ignore the
start_pad read from the nvdimm and overwrite that with zero here.
This patch doesn't enforce that right? After the next patch we can have
values other than 0 in pfn_sb->start_pad?


>
> Fixes: 32ab0a3f5170 ("libnvdimm, pmem: 'struct page' for pmem")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/nvdimm/dax_devs.c |    2 +-
>  drivers/nvdimm/pfn.h      |    1 +
>  drivers/nvdimm/pfn_devs.c |   18 +++++++++++++++---
>  3 files changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvdimm/dax_devs.c b/drivers/nvdimm/dax_devs.c
> index 49fc18ee0565..6d22b0f83b3b 100644
> --- a/drivers/nvdimm/dax_devs.c
> +++ b/drivers/nvdimm/dax_devs.c
> @@ -118,7 +118,7 @@ int nd_dax_probe(struct device *dev, struct nd_namespace_common *ndns)
>  	nvdimm_bus_unlock(&ndns->dev);
>  	if (!dax_dev)
>  		return -ENOMEM;
> -	pfn_sb = devm_kzalloc(dev, sizeof(*pfn_sb), GFP_KERNEL);
> +	pfn_sb = devm_kmalloc(dev, sizeof(*pfn_sb), GFP_KERNEL);
>  	nd_pfn->pfn_sb = pfn_sb;
>  	rc = nd_pfn_validate(nd_pfn, DAX_SIG);
>  	dev_dbg(dev, "dax: %s\n", rc == 0 ? dev_name(dax_dev) : "<none>");
> diff --git a/drivers/nvdimm/pfn.h b/drivers/nvdimm/pfn.h
> index f58b849e455b..dfb2bcda8f5a 100644
> --- a/drivers/nvdimm/pfn.h
> +++ b/drivers/nvdimm/pfn.h
> @@ -28,6 +28,7 @@ struct nd_pfn_sb {
>  	__le32 end_trunc;
>  	/* minor-version-2 record the base alignment of the mapping */
>  	__le32 align;
> +	/* minor-version-3 guarantee the padding and flags are zero */
>  	u8 padding[4000];
>  	__le64 checksum;
>  };
> diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
> index 0f81fc56bbfd..4977424693b0 100644
> --- a/drivers/nvdimm/pfn_devs.c
> +++ b/drivers/nvdimm/pfn_devs.c
> @@ -412,6 +412,15 @@ static int nd_pfn_clear_memmap_errors(struct nd_pfn *nd_pfn)
>  	return 0;
>  }
>  
> +/**
> + * nd_pfn_validate - read and validate info-block
> + * @nd_pfn: fsdax namespace runtime state / properties
> + * @sig: 'devdax' or 'fsdax' signature
> + *
> + * Upon return the info-block buffer contents (->pfn_sb) are
> + * indeterminate when validation fails, and a coherent info-block
> + * otherwise.
> + */
>  int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
>  {
>  	u64 checksum, offset;
> @@ -557,7 +566,7 @@ int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns)
>  	nvdimm_bus_unlock(&ndns->dev);
>  	if (!pfn_dev)
>  		return -ENOMEM;
> -	pfn_sb = devm_kzalloc(dev, sizeof(*pfn_sb), GFP_KERNEL);
> +	pfn_sb = devm_kmalloc(dev, sizeof(*pfn_sb), GFP_KERNEL);
>  	nd_pfn = to_nd_pfn(pfn_dev);
>  	nd_pfn->pfn_sb = pfn_sb;
>  	rc = nd_pfn_validate(nd_pfn, PFN_SIG);
> @@ -694,7 +703,7 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
>  	u64 checksum;
>  	int rc;
>  
> -	pfn_sb = devm_kzalloc(&nd_pfn->dev, sizeof(*pfn_sb), GFP_KERNEL);
> +	pfn_sb = devm_kmalloc(&nd_pfn->dev, sizeof(*pfn_sb), GFP_KERNEL);
>  	if (!pfn_sb)
>  		return -ENOMEM;
>  
> @@ -703,11 +712,14 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
>  		sig = DAX_SIG;
>  	else
>  		sig = PFN_SIG;
> +
>  	rc = nd_pfn_validate(nd_pfn, sig);
>  	if (rc != -ENODEV)
>  		return rc;
>  
>  	/* no info block, do init */;
> +	memset(pfn_sb, 0, sizeof(*pfn_sb));
> +
>  	nd_region = to_nd_region(nd_pfn->dev.parent);
>  	if (nd_region->ro) {
>  		dev_info(&nd_pfn->dev,
> @@ -760,7 +772,7 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
>  	memcpy(pfn_sb->uuid, nd_pfn->uuid, 16);
>  	memcpy(pfn_sb->parent_uuid, nd_dev_to_uuid(&ndns->dev), 16);
>  	pfn_sb->version_major = cpu_to_le16(1);
> -	pfn_sb->version_minor = cpu_to_le16(2);
> +	pfn_sb->version_minor = cpu_to_le16(3);
>  	pfn_sb->start_pad = cpu_to_le32(start_pad);
>  	pfn_sb->end_trunc = cpu_to_le32(end_trunc);
>  	pfn_sb->align = cpu_to_le32(nd_pfn->align);
>
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