nvmem: Add flag to export NVMEM to root only

Legacy AT24, AT25 EEPROMs are exported in sys so that only root can
read the contents. The EEPROMs may contain sensitive information. Add
a flag so the provide can indicate that NVMEM should also restrict
access to root only.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 56 insertions, 2 deletions

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index de14fae6f7f6..b03690bc8f09 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -161,6 +161,53 @@ static const struct attribute_group *nvmem_ro_dev_groups[] = {
         NULL,
 };
 
+/* default read/write permissions, root only */
+static struct bin_attribute bin_attr_rw_root_nvmem = {
+        .attr   = {
+                .name   = "nvmem",
+                .mode   = S_IWUSR | S_IRUSR,
+        },
+        .read   = bin_attr_nvmem_read,
+        .write  = bin_attr_nvmem_write,
+};
+
+static struct bin_attribute *nvmem_bin_rw_root_attributes[] = {
+        &bin_attr_rw_root_nvmem,
+        NULL,
+};
+
+static const struct attribute_group nvmem_bin_rw_root_group = {
+        .bin_attrs      = nvmem_bin_rw_root_attributes,
+};
+
+static const struct attribute_group *nvmem_rw_root_dev_groups[] = {
+        &nvmem_bin_rw_root_group,
+        NULL,
+};
+
+/* read only permission, root only */
+static struct bin_attribute bin_attr_ro_root_nvmem = {
+        .attr   = {
+                .name   = "nvmem",
+                .mode   = S_IRUSR,
+        },
+        .read   = bin_attr_nvmem_read,
+};
+
+static struct bin_attribute *nvmem_bin_ro_root_attributes[] = {
+        &bin_attr_ro_root_nvmem,
+        NULL,
+};
+
+static const struct attribute_group nvmem_bin_ro_root_group = {
+        .bin_attrs      = nvmem_bin_ro_root_attributes,
+};
+
+static const struct attribute_group *nvmem_ro_root_dev_groups[] = {
+        &nvmem_bin_ro_root_group,
+        NULL,
+};
+
 static void nvmem_release(struct device *dev)
 {
         struct nvmem_device *nvmem = to_nvmem_device(dev);
@@ -355,8 +402,14 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
         nvmem->read_only = of_property_read_bool(np, "read-only") |
                            config->read_only;
 
-        nvmem->dev.groups = nvmem->read_only ? nvmem_ro_dev_groups :
-                                               nvmem_rw_dev_groups;
+        if (config->root_only)
+                nvmem->dev.groups = nvmem->read_only ?
+                        nvmem_ro_root_dev_groups :
+                        nvmem_rw_root_dev_groups;
+        else
+                nvmem->dev.groups = nvmem->read_only ?
+                        nvmem_ro_dev_groups :
+                        nvmem_rw_dev_groups;
 
         device_initialize(&nvmem->dev);
 
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 0b68caff1b3c..d24fefa0c11d 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -23,6 +23,7 @@ struct nvmem_config {
         const struct nvmem_cell_info    *cells;
         int                     ncells;
         bool                    read_only;
+        bool                    root_only;
 };
 
 #if IS_ENABLED(CONFIG_NVMEM)