[RFC PATCH 0/2] fpga: improve protection against low-level modules unloading

[RFC PATCH 0/2] fpga: improve protection against low-level modules unloading

[Marco Pagani]

This RFC proposes a possible solution to keep protecting the fpga
manager against the unexpected unloading of low-level control modules
while addressing the limitations of the current implementation. The
current implementation assumes that the low-level module registers a
platform driver for the parent device, which can later be used by the
fpga manager (through the parent device pointer) to take the low-level
module's refcount. This proposal removes this limitation by adding a
module owner field to the fpga_manager and fpga_manager_ops structs.
Low-level control modules can statically set the owner field to
THIS_MODULE. Later, the fpga manager can use the owner field to take
the module's refcount.

For more context, please refer to these threads:
https://lore.kernel.org/linux-fpga/ZS6hhlvjUcqyv8zL@yilunxu-OptiPlex-7050
https://lore.kernel.org/linux-fpga/ZT9qENE9fE3Z0KCW@yilunxu-OptiPlex-7050

Signed-off-by: Marco Pagani <marpagan@redhat.com>

Marco Pagani (2):
  fpga: add a module owner field to fpga_manager and fpga_manager_ops
  fpga: set owner of fpga_manager_ops for existing low-level modules

 drivers/fpga/altera-cvp.c             |  1 +
 drivers/fpga/altera-pr-ip-core.c      |  1 +
 drivers/fpga/altera-ps-spi.c          |  1 +
 drivers/fpga/dfl-fme-mgr.c            |  1 +
 drivers/fpga/fpga-mgr.c               | 56 +++++++++++++++++++--------
 drivers/fpga/ice40-spi.c              |  1 +
 drivers/fpga/lattice-sysconfig.c      |  1 +
 drivers/fpga/machxo2-spi.c            |  1 +
 drivers/fpga/microchip-spi.c          |  1 +
 drivers/fpga/socfpga-a10.c            |  1 +
 drivers/fpga/socfpga.c                |  1 +
 drivers/fpga/stratix10-soc.c          |  1 +
 drivers/fpga/tests/fpga-mgr-test.c    |  1 +
 drivers/fpga/tests/fpga-region-test.c |  1 +
 drivers/fpga/ts73xx-fpga.c            |  1 +
 drivers/fpga/versal-fpga.c            |  1 +
 drivers/fpga/xilinx-spi.c             |  1 +
 drivers/fpga/zynq-fpga.c              |  1 +
 drivers/fpga/zynqmp-fpga.c            |  1 +
 include/linux/fpga/fpga-mgr.h         |  4 ++
 20 files changed, 62 insertions(+), 16 deletions(-)


base-commit: 98b1cc82c4affc16f5598d4fa14b1858671b2263
-- 
2.42.0

[RFC PATCH 1/2] fpga: add a module owner field to fpga_manager and fpga_manager_ops

[Marco Pagani]

Add a module *owner field to the fpga_manager_ops and fpga_manager
structs to protect the fpga manager against the unloading of the
low-level control module while someone is holding a reference to the
manager device. Low-level control modules should statically set the
owner field of the fpga_manager_ops struct to THIS_MODULE. Then, when
the manager is registered using fpga_mgr_register(), the value is copied
into the owner field of the fpga_manager struct (that contains the
device context). In this way, the manager can later use it in
fpga_mgr_get() to take the low-level module's refcount. To prevent races
while unloading the low-level control module, the fpga_mgr_get() and
fpga_mgr_put() methods are protected with a mutex.

Other changes: moved put_device() form __fpga_mgr_get() to
fpga_mgr_get() and of_fpga_mgr_get() to improve code clarity.

Fixes: 654ba4cc0f3e ("fpga manager: ensure lifetime with of_fpga_mgr_get")
Signed-off-by: Marco Pagani <marpagan@redhat.com>
---
 drivers/fpga/fpga-mgr.c       | 56 +++++++++++++++++++++++++----------
 include/linux/fpga/fpga-mgr.h |  4 +++
 2 files changed, 44 insertions(+), 16 deletions(-)

diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
index 06651389c592..f76be7e2f722 100644
--- a/drivers/fpga/fpga-mgr.c
+++ b/drivers/fpga/fpga-mgr.c
@@ -21,6 +21,8 @@
 static DEFINE_IDA(fpga_mgr_ida);
 static const struct class fpga_mgr_class;
 
+static DEFINE_MUTEX(mgr_lock);
+
 struct fpga_mgr_devres {
 	struct fpga_manager *mgr;
 };
@@ -667,17 +669,15 @@ ATTRIBUTE_GROUPS(fpga_mgr);
 static struct fpga_manager *__fpga_mgr_get(struct device *dev)
 {
 	struct fpga_manager *mgr;
+	struct module *owner;
 
 	mgr = to_fpga_manager(dev);
+	owner = mgr->owner;
 
-	if (!try_module_get(dev->parent->driver->owner))
-		goto err_dev;
+	if (owner && !try_module_get(owner))
+		mgr = ERR_PTR(-ENODEV);
 
 	return mgr;
-
-err_dev:
-	put_device(dev);
-	return ERR_PTR(-ENODEV);
 }
 
 static int fpga_mgr_dev_match(struct device *dev, const void *data)
@@ -693,12 +693,22 @@ static int fpga_mgr_dev_match(struct device *dev, const void *data)
  */
 struct fpga_manager *fpga_mgr_get(struct device *dev)
 {
-	struct device *mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev,
-						   fpga_mgr_dev_match);
+	struct fpga_manager *mgr = ERR_PTR(-ENODEV);
+	struct device *mgr_dev;
+
+	mutex_lock(&mgr_lock);
+
+	mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev, fpga_mgr_dev_match);
 	if (!mgr_dev)
-		return ERR_PTR(-ENODEV);
+		goto out;
+
+	mgr = __fpga_mgr_get(mgr_dev);
+	if (IS_ERR(mgr))
+		put_device(mgr_dev);
 
-	return __fpga_mgr_get(mgr_dev);
+out:
+	mutex_unlock(&mgr_lock);
+	return mgr;
 }
 EXPORT_SYMBOL_GPL(fpga_mgr_get);
 
@@ -711,13 +721,22 @@ EXPORT_SYMBOL_GPL(fpga_mgr_get);
  */
 struct fpga_manager *of_fpga_mgr_get(struct device_node *node)
 {
-	struct device *dev;
+	struct fpga_manager *mgr = ERR_PTR(-ENODEV);
+	struct device *mgr_dev;
+
+	mutex_lock(&mgr_lock);
+
+	mgr_dev = class_find_device_by_of_node(&fpga_mgr_class, node);
+	if (!mgr_dev)
+		goto out;
 
-	dev = class_find_device_by_of_node(&fpga_mgr_class, node);
-	if (!dev)
-		return ERR_PTR(-ENODEV);
+	mgr = __fpga_mgr_get(mgr_dev);
+	if (IS_ERR(mgr))
+		put_device(mgr_dev);
 
-	return __fpga_mgr_get(dev);
+out:
+	mutex_unlock(&mgr_lock);
+	return mgr;
 }
 EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
 
@@ -727,8 +746,12 @@ EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
  */
 void fpga_mgr_put(struct fpga_manager *mgr)
 {
-	module_put(mgr->dev.parent->driver->owner);
+	mutex_lock(&mgr_lock);
+
+	module_put(mgr->owner);
 	put_device(&mgr->dev);
+
+	mutex_unlock(&mgr_lock);
 }
 EXPORT_SYMBOL_GPL(fpga_mgr_put);
 
@@ -806,6 +829,7 @@ fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *in
 
 	mgr->name = info->name;
 	mgr->mops = info->mops;
+	mgr->owner = info->mops->owner;
 	mgr->priv = info->priv;
 	mgr->compat_id = info->compat_id;
 
diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index 54f63459efd6..eaf6e072dbc0 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -162,6 +162,7 @@ struct fpga_manager_info {
  * @write_complete: set FPGA to operating state after writing is done
  * @fpga_remove: optional: Set FPGA into a specific state during driver remove
  * @groups: optional attribute groups.
+ * @owner: owner module.
  *
  * fpga_manager_ops are the low level functions implemented by a specific
  * fpga manager driver.  The optional ones are tested for NULL before being
@@ -184,6 +185,7 @@ struct fpga_manager_ops {
 			      struct fpga_image_info *info);
 	void (*fpga_remove)(struct fpga_manager *mgr);
 	const struct attribute_group **groups;
+	struct module *owner;
 };
 
 /* FPGA manager status: Partial/Full Reconfiguration errors */
@@ -201,6 +203,7 @@ struct fpga_manager_ops {
  * @state: state of fpga manager
  * @compat_id: FPGA manager id for compatibility check.
  * @mops: pointer to struct of fpga manager ops
+ * @owner: owner module.
  * @priv: low level driver private date
  */
 struct fpga_manager {
@@ -210,6 +213,7 @@ struct fpga_manager {
 	enum fpga_mgr_states state;
 	struct fpga_compat_id *compat_id;
 	const struct fpga_manager_ops *mops;
+	struct module *owner;
 	void *priv;
 };
 
-- 
2.42.0

[RFC PATCH 2/2] fpga: set owner of fpga_manager_ops for existing low-level modules

[Marco Pagani]

This patch tentatively set the owner field of fpga_manager_ops to
THIS_MODULE for existing fpga manager low-level control modules.

Signed-off-by: Marco Pagani <marpagan@redhat.com>
---
 drivers/fpga/altera-cvp.c             | 1 +
 drivers/fpga/altera-pr-ip-core.c      | 1 +
 drivers/fpga/altera-ps-spi.c          | 1 +
 drivers/fpga/dfl-fme-mgr.c            | 1 +
 drivers/fpga/ice40-spi.c              | 1 +
 drivers/fpga/lattice-sysconfig.c      | 1 +
 drivers/fpga/machxo2-spi.c            | 1 +
 drivers/fpga/microchip-spi.c          | 1 +
 drivers/fpga/socfpga-a10.c            | 1 +
 drivers/fpga/socfpga.c                | 1 +
 drivers/fpga/stratix10-soc.c          | 1 +
 drivers/fpga/tests/fpga-mgr-test.c    | 1 +
 drivers/fpga/tests/fpga-region-test.c | 1 +
 drivers/fpga/ts73xx-fpga.c            | 1 +
 drivers/fpga/versal-fpga.c            | 1 +
 drivers/fpga/xilinx-spi.c             | 1 +
 drivers/fpga/zynq-fpga.c              | 1 +
 drivers/fpga/zynqmp-fpga.c            | 1 +
 18 files changed, 18 insertions(+)

diff --git a/drivers/fpga/altera-cvp.c b/drivers/fpga/altera-cvp.c
index 4ffb9da537d8..aeb913547dd8 100644
--- a/drivers/fpga/altera-cvp.c
+++ b/drivers/fpga/altera-cvp.c
@@ -520,6 +520,7 @@ static const struct fpga_manager_ops altera_cvp_ops = {
 	.write_init	= altera_cvp_write_init,
 	.write		= altera_cvp_write,
 	.write_complete	= altera_cvp_write_complete,
+	.owner		= THIS_MODULE,
 };
 
 static const struct cvp_priv cvp_priv_v1 = {
diff --git a/drivers/fpga/altera-pr-ip-core.c b/drivers/fpga/altera-pr-ip-core.c
index df8671af4a92..354221c609e6 100644
--- a/drivers/fpga/altera-pr-ip-core.c
+++ b/drivers/fpga/altera-pr-ip-core.c
@@ -171,6 +171,7 @@ static const struct fpga_manager_ops alt_pr_ops = {
 	.write_init = alt_pr_fpga_write_init,
 	.write = alt_pr_fpga_write,
 	.write_complete = alt_pr_fpga_write_complete,
+	.owner = THIS_MODULE,
 };
 
 int alt_pr_register(struct device *dev, void __iomem *reg_base)
diff --git a/drivers/fpga/altera-ps-spi.c b/drivers/fpga/altera-ps-spi.c
index 740980e7cef8..3be05796a6fc 100644
--- a/drivers/fpga/altera-ps-spi.c
+++ b/drivers/fpga/altera-ps-spi.c
@@ -228,6 +228,7 @@ static const struct fpga_manager_ops altera_ps_ops = {
 	.write_init = altera_ps_write_init,
 	.write = altera_ps_write,
 	.write_complete = altera_ps_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int altera_ps_probe(struct spi_device *spi)
diff --git a/drivers/fpga/dfl-fme-mgr.c b/drivers/fpga/dfl-fme-mgr.c
index ab228d8837a0..740ce82e3ac9 100644
--- a/drivers/fpga/dfl-fme-mgr.c
+++ b/drivers/fpga/dfl-fme-mgr.c
@@ -264,6 +264,7 @@ static const struct fpga_manager_ops fme_mgr_ops = {
 	.write = fme_mgr_write,
 	.write_complete = fme_mgr_write_complete,
 	.status = fme_mgr_status,
+	.owner = THIS_MODULE,
 };
 
 static void fme_mgr_get_compat_id(void __iomem *fme_pr,
diff --git a/drivers/fpga/ice40-spi.c b/drivers/fpga/ice40-spi.c
index 7cbb3558b844..97afa6dc5d76 100644
--- a/drivers/fpga/ice40-spi.c
+++ b/drivers/fpga/ice40-spi.c
@@ -130,6 +130,7 @@ static const struct fpga_manager_ops ice40_fpga_ops = {
 	.write_init = ice40_fpga_ops_write_init,
 	.write = ice40_fpga_ops_write,
 	.write_complete = ice40_fpga_ops_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int ice40_fpga_probe(struct spi_device *spi)
diff --git a/drivers/fpga/lattice-sysconfig.c b/drivers/fpga/lattice-sysconfig.c
index ba51a60f672f..1393cdd11e49 100644
--- a/drivers/fpga/lattice-sysconfig.c
+++ b/drivers/fpga/lattice-sysconfig.c
@@ -348,6 +348,7 @@ static const struct fpga_manager_ops sysconfig_fpga_mgr_ops = {
 	.write_init = sysconfig_ops_write_init,
 	.write = sysconfig_ops_write,
 	.write_complete = sysconfig_ops_write_complete,
+	.owner = THIS_MODULE,
 };
 
 int sysconfig_probe(struct sysconfig_priv *priv)
diff --git a/drivers/fpga/machxo2-spi.c b/drivers/fpga/machxo2-spi.c
index 905607992a12..46193a47f863 100644
--- a/drivers/fpga/machxo2-spi.c
+++ b/drivers/fpga/machxo2-spi.c
@@ -358,6 +358,7 @@ static const struct fpga_manager_ops machxo2_ops = {
 	.write_init = machxo2_write_init,
 	.write = machxo2_write,
 	.write_complete = machxo2_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int machxo2_spi_probe(struct spi_device *spi)
diff --git a/drivers/fpga/microchip-spi.c b/drivers/fpga/microchip-spi.c
index 2a82c726d6e5..023ccdf2d5da 100644
--- a/drivers/fpga/microchip-spi.c
+++ b/drivers/fpga/microchip-spi.c
@@ -362,6 +362,7 @@ static const struct fpga_manager_ops mpf_ops = {
 	.write_init = mpf_ops_write_init,
 	.write = mpf_ops_write,
 	.write_complete = mpf_ops_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int mpf_probe(struct spi_device *spi)
diff --git a/drivers/fpga/socfpga-a10.c b/drivers/fpga/socfpga-a10.c
index cc4861e345c9..a8ab74b30006 100644
--- a/drivers/fpga/socfpga-a10.c
+++ b/drivers/fpga/socfpga-a10.c
@@ -463,6 +463,7 @@ static const struct fpga_manager_ops socfpga_a10_fpga_mgr_ops = {
 	.write_init = socfpga_a10_fpga_write_init,
 	.write = socfpga_a10_fpga_write,
 	.write_complete = socfpga_a10_fpga_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int socfpga_a10_fpga_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/socfpga.c b/drivers/fpga/socfpga.c
index 723ea0ad3f09..87f3f4a367d0 100644
--- a/drivers/fpga/socfpga.c
+++ b/drivers/fpga/socfpga.c
@@ -538,6 +538,7 @@ static const struct fpga_manager_ops socfpga_fpga_ops = {
 	.write_init = socfpga_fpga_ops_configure_init,
 	.write = socfpga_fpga_ops_configure_write,
 	.write_complete = socfpga_fpga_ops_configure_complete,
+	.owner = THIS_MODULE,
 };
 
 static int socfpga_fpga_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/stratix10-soc.c b/drivers/fpga/stratix10-soc.c
index cacb9cc5757e..63a5a2fe4911 100644
--- a/drivers/fpga/stratix10-soc.c
+++ b/drivers/fpga/stratix10-soc.c
@@ -393,6 +393,7 @@ static const struct fpga_manager_ops s10_ops = {
 	.write_init = s10_ops_write_init,
 	.write = s10_ops_write,
 	.write_complete = s10_ops_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int s10_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/tests/fpga-mgr-test.c b/drivers/fpga/tests/fpga-mgr-test.c
index 6acec55b60ce..4c2a3e98f8ad 100644
--- a/drivers/fpga/tests/fpga-mgr-test.c
+++ b/drivers/fpga/tests/fpga-mgr-test.c
@@ -187,6 +187,7 @@ static const struct fpga_manager_ops fake_mgr_ops = {
 	.write = op_write,
 	.write_sg = op_write_sg,
 	.write_complete = op_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static void fpga_mgr_test_get(struct kunit *test)
diff --git a/drivers/fpga/tests/fpga-region-test.c b/drivers/fpga/tests/fpga-region-test.c
index baab07e3fc59..2705c1b33d09 100644
--- a/drivers/fpga/tests/fpga-region-test.c
+++ b/drivers/fpga/tests/fpga-region-test.c
@@ -52,6 +52,7 @@ static int op_write(struct fpga_manager *mgr, const char *buf, size_t count)
  */
 static const struct fpga_manager_ops fake_mgr_ops = {
 	.write = op_write,
+	.owner = THIS_MODULE,
 };
 
 static int op_enable_set(struct fpga_bridge *bridge, bool enable)
diff --git a/drivers/fpga/ts73xx-fpga.c b/drivers/fpga/ts73xx-fpga.c
index 4e1d2a4d3df4..20b8db0d150a 100644
--- a/drivers/fpga/ts73xx-fpga.c
+++ b/drivers/fpga/ts73xx-fpga.c
@@ -96,6 +96,7 @@ static const struct fpga_manager_ops ts73xx_fpga_ops = {
 	.write_init	= ts73xx_fpga_write_init,
 	.write		= ts73xx_fpga_write,
 	.write_complete	= ts73xx_fpga_write_complete,
+	.owner		= THIS_MODULE,
 };
 
 static int ts73xx_fpga_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/versal-fpga.c b/drivers/fpga/versal-fpga.c
index 3710e8f01be2..02fd8ed36ff0 100644
--- a/drivers/fpga/versal-fpga.c
+++ b/drivers/fpga/versal-fpga.c
@@ -40,6 +40,7 @@ static int versal_fpga_ops_write(struct fpga_manager *mgr,
 static const struct fpga_manager_ops versal_fpga_ops = {
 	.write_init = versal_fpga_ops_write_init,
 	.write = versal_fpga_ops_write,
+	.owner = THIS_MODULE,
 };
 
 static int versal_fpga_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/xilinx-spi.c b/drivers/fpga/xilinx-spi.c
index e1a227e7ff2a..d58cf0ccbd41 100644
--- a/drivers/fpga/xilinx-spi.c
+++ b/drivers/fpga/xilinx-spi.c
@@ -218,6 +218,7 @@ static const struct fpga_manager_ops xilinx_spi_ops = {
 	.write_init = xilinx_spi_write_init,
 	.write = xilinx_spi_write,
 	.write_complete = xilinx_spi_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int xilinx_spi_probe(struct spi_device *spi)
diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
index 96611d424a10..241e1fe48a13 100644
--- a/drivers/fpga/zynq-fpga.c
+++ b/drivers/fpga/zynq-fpga.c
@@ -548,6 +548,7 @@ static const struct fpga_manager_ops zynq_fpga_ops = {
 	.write_init = zynq_fpga_ops_write_init,
 	.write_sg = zynq_fpga_ops_write,
 	.write_complete = zynq_fpga_ops_write_complete,
+	.owner = THIS_MODULE,
 };
 
 static int zynq_fpga_probe(struct platform_device *pdev)
diff --git a/drivers/fpga/zynqmp-fpga.c b/drivers/fpga/zynqmp-fpga.c
index f3434e2c487b..2f66400d2330 100644
--- a/drivers/fpga/zynqmp-fpga.c
+++ b/drivers/fpga/zynqmp-fpga.c
@@ -101,6 +101,7 @@ static const struct fpga_manager_ops zynqmp_fpga_ops = {
 	.state = zynqmp_fpga_ops_state,
 	.write_init = zynqmp_fpga_ops_write_init,
 	.write = zynqmp_fpga_ops_write,
+	.owner = THIS_MODULE,
 };
 
 static int zynqmp_fpga_probe(struct platform_device *pdev)
-- 
2.42.0