From: Dan Williams dan.j.williams@intel.com Subject: libnvdimm/pfn: fix fsdax-mode namespace info-block zero-fields

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.

Link: http://lkml.kernel.org/r/156092356065.979959.6681003754765958296.stgit@dwill... Fixes: 32ab0a3f5170 ("libnvdimm, pmem: 'struct page' for pmem") Signed-off-by: Dan Williams dan.j.williams@intel.com Tested-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com [ppc64] Cc: stable@vger.kernel.org Cc: David Hildenbrand david@redhat.com Cc: Jane Chu jane.chu@oracle.com Cc: Jeff Moyer jmoyer@redhat.com Cc: Jérôme Glisse jglisse@redhat.com Cc: Jonathan Corbet corbet@lwn.net Cc: Logan Gunthorpe logang@deltatee.com Cc: Michal Hocko mhocko@suse.com Cc: Mike Rapoport rppt@linux.ibm.com Cc: Oscar Salvador osalvador@suse.de Cc: Pavel Tatashin pasha.tatashin@soleen.com Cc: Toshi Kani toshi.kani@hpe.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Wei Yang richardw.yang@linux.intel.com Cc: Jason Gunthorpe jgg@mellanox.com Cc: Christoph Hellwig hch@lst.de Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

drivers/nvdimm/dax_devs.c | 2 +- drivers/nvdimm/pfn.h | 1 + drivers/nvdimm/pfn_devs.c | 18 +++++++++++++++--- 3 files changed, 17 insertions(+), 4 deletions(-)

--- a/drivers/nvdimm/dax_devs.c~libnvdimm-pfn-fix-fsdax-mode-namespace-info-block-zero-fields +++ a/drivers/nvdimm/dax_devs.c @@ -118,7 +118,7 @@ int nd_dax_probe(struct device *dev, str 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>"); --- a/drivers/nvdimm/pfn_devs.c~libnvdimm-pfn-fix-fsdax-mode-namespace-info-block-zero-fields +++ a/drivers/nvdimm/pfn_devs.c @@ -412,6 +412,15 @@ static int nd_pfn_clear_memmap_errors(st 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, str 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); @@ -693,7 +702,7 @@ static int nd_pfn_init(struct nd_pfn *nd 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;

@@ -702,11 +711,14 @@ static int nd_pfn_init(struct nd_pfn *nd 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, @@ -759,7 +771,7 @@ static int nd_pfn_init(struct nd_pfn *nd 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); --- a/drivers/nvdimm/pfn.h~libnvdimm-pfn-fix-fsdax-mode-namespace-info-block-zero-fields +++ a/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; }; _