libnvdimm/pfn: fix fsdax-mode namespace info-block zero-fields [Linux 4.9.187]

This Linux kernel change "libnvdimm/pfn: fix fsdax-mode namespace info-block zero-fields" is included in the Linux 4.9.187 release. This change is authored by Dan Williams <dan.j.williams [at]> on Thu Jul 18 15:58:36 2019 -0700. The commit for this change in Linux stable tree is 7839be2 (patch) which is from upstream commit 7e3e888. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream 7e3e888.

libnvdimm/pfn: fix fsdax-mode namespace info-block zero-fields

commit 7e3e888dfc138089f4c15a81b418e88f0978f744 upstream.

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.

Fixes: 32ab0a3f5170 ("libnvdimm, pmem: 'struct page' for pmem")
Signed-off-by: Dan Williams <>
Tested-by: Aneesh Kumar K.V <>    [ppc64]
Cc: <>
Cc: David Hildenbrand <>
Cc: Jane Chu <>
Cc: Jeff Moyer <>
Cc: Jérôme Glisse <>
Cc: Jonathan Corbet <>
Cc: Logan Gunthorpe <>
Cc: Michal Hocko <>
Cc: Mike Rapoport <>
Cc: Oscar Salvador <>
Cc: Pavel Tatashin <>
Cc: Toshi Kani <>
Cc: Vlastimil Babka <>
Cc: Wei Yang <>
Cc: Jason Gunthorpe <>
Cc: Christoph Hellwig <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

There are 21 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 45fa82c..da50466 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)
    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, "%s: dax: %s\n", __func__,
diff --git a/drivers/nvdimm/pfn.h b/drivers/nvdimm/pfn.h
index dde9853..e901e3a 100644
--- a/drivers/nvdimm/pfn.h
+++ b/drivers/nvdimm/pfn.h
@@ -36,6 +36,7 @@ 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 ba9aa84..f40c9c6 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -349,6 +349,15 @@ struct device *nd_pfn_create(struct nd_region *nd_region)
    return dev;

+ * 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;
@@ -486,7 +495,7 @@ int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns)
    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);
@@ -584,7 +593,7 @@ 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;

@@ -593,11 +602,14 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
        sig = DAX_SIG;
        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) {
@@ -673,7 +685,7 @@ 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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