Re: [PATCH v3 1/1] of: unittest: overlay: ensure proper alignment of copied FDT

[Guenter Roeck]

On 4/8/21 8:17 AM, frowand.list@xxxxxxxxx wrote:
> From: Frank Rowand <frank.rowand@xxxxxxxx>
> 
> The Devicetree standard specifies an 8 byte alignment of the FDT.
> Code in libfdt expects this alignment for an FDT image in memory.
> kmemdup() returns 4 byte alignment on openrisc.  Replace kmemdup()
> with kmalloc(), align pointer, memcpy() to get proper alignment.
> 
> The 4 byte alignment exposed a related bug which triggered a crash
> on openrisc with:
> commit 79edff12060f ("scripts/dtc: Update to upstream version v1.6.0-51-g183df9e9c2b9")
> as reported in:
> https://lore.kernel.org/lkml/20210327224116.69309-1-linux@xxxxxxxxxxxx/
> 
> Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>
> ---
> 
> changes since version 1:
>   - use pointer from kmalloc() for kfree() instead of using pointer that
>     has been modified for FDT alignment
> 
> changes since version 2:
>   - version 1 was a work in progress version, I failed to commit the following
>     final changes
>   - reorder first two arguments of of_overlay_apply()
> 
>  drivers/of/of_private.h |  2 ++
>  drivers/of/overlay.c    | 28 +++++++++++++++++-----------
>  drivers/of/unittest.c   | 12 +++++++++---
>  3 files changed, 28 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
> index d9e6a324de0a..d717efbd637d 100644
> --- a/drivers/of/of_private.h
> +++ b/drivers/of/of_private.h
> @@ -8,6 +8,8 @@
>   * Copyright (C) 1996-2005 Paul Mackerras.
>   */
>  
> +#define FDT_ALIGN_SIZE 8
> +

Use existing define ? Or was that local in libfdt ?

>  /**
>   * struct alias_prop - Alias property in 'aliases' node
>   * @link:	List node to link the structure in aliases_lookup list
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 50bbe0edf538..cf770452e1e5 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -57,7 +57,7 @@ struct fragment {
>   * struct overlay_changeset
>   * @id:			changeset identifier
>   * @ovcs_list:		list on which we are located
> - * @fdt:		FDT that was unflattened to create @overlay_tree
> + * @fdt:		base of memory allocated to hold aligned FDT that was unflattened to create @overlay_tree
>   * @overlay_tree:	expanded device tree that contains the fragment nodes
>   * @count:		count of fragment structures
>   * @fragments:		fragment nodes in the overlay expanded device tree
> @@ -719,8 +719,8 @@ static struct device_node *find_target(struct device_node *info_node)
>  /**
>   * init_overlay_changeset() - initialize overlay changeset from overlay tree
>   * @ovcs:	Overlay changeset to build
> - * @fdt:	the FDT that was unflattened to create @tree
> - * @tree:	Contains all the overlay fragments and overlay fixup nodes
> + * @fdt:	base of memory allocated to hold aligned FDT that was unflattened to create @tree
> + * @tree:	Contains the overlay fragments and overlay fixup nodes
>   *
>   * Initialize @ovcs.  Populate @ovcs->fragments with node information from
>   * the top level of @tree.  The relevant top level nodes are the fragment
> @@ -873,7 +873,8 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>   * internal documentation
>   *
>   * of_overlay_apply() - Create and apply an overlay changeset
> - * @fdt:	the FDT that was unflattened to create @tree
> + * @fdt:	base of memory allocated to hold *@fdt_align
> + * @fdt_align:	the FDT that was unflattened to create @tree, aligned
>   * @tree:	Expanded overlay device tree
>   * @ovcs_id:	Pointer to overlay changeset id
>   *
> @@ -912,8 +913,8 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>   * id is returned to *ovcs_id.
>   */
>  
> -static int of_overlay_apply(const void *fdt, struct device_node *tree,
> -		int *ovcs_id)
> +static int of_overlay_apply(const void *fdt, const void *fdt_align,

fdt_align is not used in this function.

> +		struct device_node *tree, int *ovcs_id)
>  {
>  	struct overlay_changeset *ovcs;
>  	int ret = 0, ret_revert, ret_tmp;
> @@ -953,7 +954,7 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
>  	/*
>  	 * after overlay_notify(), ovcs->overlay_tree related pointers may have
>  	 * leaked to drivers, so can not kfree() tree, aka ovcs->overlay_tree;
> -	 * and can not free fdt, aka ovcs->fdt
> +	 * and can not free memory containing aligned fdt, aka ovcs->fdt

ovcs->fdt does not point to the aligned fdt, but to the allocated fdt.

>  	 */
>  	ret = overlay_notify(ovcs, OF_OVERLAY_PRE_APPLY);
>  	if (ret) {
> @@ -1014,7 +1015,8 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
>  int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>  			 int *ovcs_id)
>  {
> -	const void *new_fdt;
> +	void *new_fdt;
> +	void *new_fdt_align;
>  	int ret;
>  	u32 size;
>  	struct device_node *overlay_root;
> @@ -1036,18 +1038,22 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>  	 * Must create permanent copy of FDT because of_fdt_unflatten_tree()
>  	 * will create pointers to the passed in FDT in the unflattened tree.
>  	 */
> -	new_fdt = kmemdup(overlay_fdt, size, GFP_KERNEL);
> +	size += FDT_ALIGN_SIZE;
> +	new_fdt = kmalloc(size, GFP_KERNEL);
>  	if (!new_fdt)
>  		return -ENOMEM;
>  
> -	of_fdt_unflatten_tree(new_fdt, NULL, &overlay_root);
> +	new_fdt_align = PTR_ALIGN(new_fdt, FDT_ALIGN_SIZE);
> +	memcpy(new_fdt_align, overlay_fdt, size);

Still copies beyond end of buffer.

> +
> +	of_fdt_unflatten_tree(new_fdt_align, NULL, &overlay_root);
>  	if (!overlay_root) {
>  		pr_err("unable to unflatten overlay_fdt\n");
>  		ret = -EINVAL;
>  		goto out_free_new_fdt;
>  	}
>  
> -	ret = of_overlay_apply(new_fdt, overlay_root, ovcs_id);
> +	ret = of_overlay_apply(new_fdt, new_fdt_align, overlay_root, ovcs_id);
>  	if (ret < 0) {
>  		/*
>  		 * new_fdt and overlay_root now belong to the overlay
> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> index eb100627c186..29081a8b32e6 100644
> --- a/drivers/of/unittest.c
> +++ b/drivers/of/unittest.c
> @@ -22,6 +22,7 @@
>  #include <linux/slab.h>
>  #include <linux/device.h>
>  #include <linux/platform_device.h>
> +#include <linux/kernel.h>
>  
>  #include <linux/i2c.h>
>  #include <linux/i2c-mux.h>
> @@ -1408,6 +1409,7 @@ static void attach_node_and_children(struct device_node *np)
>  static int __init unittest_data_add(void)
>  {
>  	void *unittest_data;
> +	void *unittest_data_align;
>  	struct device_node *unittest_data_node, *np;
>  	/*
>  	 * __dtb_testcases_begin[] and __dtb_testcases_end[] are magically
> @@ -1415,7 +1417,7 @@ static int __init unittest_data_add(void)
>  	 */
>  	extern uint8_t __dtb_testcases_begin[];
>  	extern uint8_t __dtb_testcases_end[];
> -	const int size = __dtb_testcases_end - __dtb_testcases_begin;
> +	u32 size = __dtb_testcases_end - __dtb_testcases_begin;
>  	int rc;
>  
>  	if (!size) {
> @@ -1425,11 +1427,15 @@ static int __init unittest_data_add(void)
>  	}
>  
>  	/* creating copy */
> -	unittest_data = kmemdup(__dtb_testcases_begin, size, GFP_KERNEL);
> +	size += FDT_ALIGN_SIZE;
> +	unittest_data = kmalloc(size, GFP_KERNEL);
>  	if (!unittest_data)
>  		return -ENOMEM;
>  
> -	of_fdt_unflatten_tree(unittest_data, NULL, &unittest_data_node);
> +	unittest_data_align = PTR_ALIGN(unittest_data, FDT_ALIGN_SIZE);
> +	memcpy(unittest_data_align, __dtb_testcases_begin, size);

Same as above.

> +
> +	of_fdt_unflatten_tree(unittest_data_align, NULL, &unittest_data_node);
>  	if (!unittest_data_node) {
>  		pr_warn("%s: No tree to attach; not running tests\n", __func__);
>  		kfree(unittest_data);
>