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

Aneesh Kumar K.V
2019-06-19T16:30:29Z

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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