linux-kernel - Re: [PATCH v2] nvmem: core: Set no-read-write provider to avoid userspace read/write

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Date:   Fri, 22 Mar 2019 15:02:11 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Gaurav Kohli <gkohli@...eaurora.org>, linux-kernel@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2] nvmem: core: Set no-read-write provider to avoid
 userspace read/write



On 20/03/2019 17:50, Gaurav Kohli wrote:
> 
>> Is root only option not helping you in this case?
> Yes we want to protect at root level as well, i mean it is better if we 
> can avoid exposing to userspace at all.
Can you try below patch!

>>
>> We could go down the route of adding new config option something like 
>> CONFIG_NVMEM_NO_SYSFS_ENTRY to prevent adding nvmem entry in userspace.
>>
>> Let me know if you are happy to create a patch for this change?
> 
> I am happy with either way config option or dt binding(seems easy), 
> please let me know we will post new patch for the same.
DT way is totally NAK.


--------------------------->cut<-----------------------------------

From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Date: Wed, 20 Mar 2019 16:15:21 +0000
Subject: [PATCH] nvmem: core: add support to NVMEM_NO_SYSFS_ENTRY

Some users might not want to expose nvmem entry to sysfs and
only intend to use kernel interface so add such provision.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
---
  Documentation/ABI/stable/sysfs-bus-nvmem |  2 ++
  drivers/nvmem/Kconfig                    |  5 +++++
  drivers/nvmem/core.c                     | 11 ++++++-----
  3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-bus-nvmem 
b/Documentation/ABI/stable/sysfs-bus-nvmem
index 5923ab4620c5..12aab0a85fea 100644
--- a/Documentation/ABI/stable/sysfs-bus-nvmem
+++ b/Documentation/ABI/stable/sysfs-bus-nvmem
@@ -6,6 +6,8 @@ Description:
  		This file allows user to read/write the raw NVMEM contents.
  		Permissions for write to this file depends on the nvmem
  		provider configuration.
+		Note: This file is not present if CONFIG_NVMEM_NO_SYSFS_ENTRY
+		is enabled

  		ex:
  		hexdump /sys/bus/nvmem/devices/qfprom0/nvmem
diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 0a7a470ee859..6ab3276d287c 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -192,4 +192,9 @@ config SC27XX_EFUSE
  	  This driver can also be built as a module. If so, the module
  	  will be called nvmem-sc27xx-efuse.

+config NVMEM_NO_SYSFS_ENTRY
+	bool "No nvmem sysfs entry"
+
+	help
+		Say Yes if you do not want to add nvmem entry to sysfs.
  endif
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index b9a0270883a0..c70f183fe379 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -216,7 +216,7 @@ static const struct attribute_group 
nvmem_bin_rw_group = {
  	.attrs		= nvmem_attrs,
  };

-static const struct attribute_group *nvmem_rw_dev_groups[] = {
+static const __maybe_unused struct attribute_group 
*nvmem_rw_dev_groups[] = {
  	&nvmem_bin_rw_group,
  	NULL,
  };
@@ -240,7 +240,7 @@ static const struct attribute_group 
nvmem_bin_ro_group = {
  	.attrs		= nvmem_attrs,
  };

-static const struct attribute_group *nvmem_ro_dev_groups[] = {
+static const __maybe_unused struct attribute_group 
*nvmem_ro_dev_groups[] = {
  	&nvmem_bin_ro_group,
  	NULL,
  };
@@ -265,7 +265,7 @@ static const struct attribute_group 
nvmem_bin_rw_root_group = {
  	.attrs		= nvmem_attrs,
  };

-static const struct attribute_group *nvmem_rw_root_dev_groups[] = {
+static const __maybe_unused struct attribute_group 
*nvmem_rw_root_dev_groups[] = {
  	&nvmem_bin_rw_root_group,
  	NULL,
  };
@@ -289,7 +289,7 @@ static const struct attribute_group 
nvmem_bin_ro_root_group = {
  	.attrs		= nvmem_attrs,
  };

-static const struct attribute_group *nvmem_ro_root_dev_groups[] = {
+static const __maybe_unused struct attribute_group 
*nvmem_ro_root_dev_groups[] = {
  	&nvmem_bin_ro_root_group,
  	NULL,
  };
@@ -688,6 +688,7 @@ struct nvmem_device *nvmem_register(const struct 
nvmem_config *config)
  	nvmem->read_only = device_property_present(config->dev, "read-only") |
  			   config->read_only;

+#if !defined(CONFIG_NVMEM_NO_SYSFS_ENTRY)
  	if (config->root_only)
  		nvmem->dev.groups = nvmem->read_only ?
  			nvmem_ro_root_dev_groups :
@@ -696,7 +697,7 @@ struct nvmem_device *nvmem_register(const struct 
nvmem_config *config)
  		nvmem->dev.groups = nvmem->read_only ?
  			nvmem_ro_dev_groups :
  			nvmem_rw_dev_groups;
-
+#endif
  	device_initialize(&nvmem->dev);

  	dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
-- 
2.21.0

--------------------------->cut<-----------------------------------