Re: [PATCH v4 1/1] of: unittest: overlay: ensure proper alignment of copied FDT
From: Frank Rowand
Date: Thu Apr 08 2021 - 18:40:18 EST
On 4/8/21 4:28 PM, Rob Herring wrote:
> On Thu, Apr 8, 2021 at 3:45 PM <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()
>>
>> changes since version 3:
>> - size of memory allocation and size of copy after pointer alignment
>> differ, use separate variables with correct values for each case
>> - edit comment to more clearly describe that ovcs->fdt is the allocated
>> memory region, which may be different than where the aligned pointer points
>> - remove unused parameter from of_overlay_apply()
>>
>> drivers/of/of_private.h | 2 ++
>> drivers/of/overlay.c | 27 +++++++++++++++++----------
>> drivers/of/unittest.c | 13 ++++++++++---
>> 3 files changed, 29 insertions(+), 13 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
>> +
>> /**
>> * 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..ecf967c57900 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 +873,7 @@ 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 the aligned FDT
>> * @tree: Expanded overlay device tree
>> * @ovcs_id: Pointer to overlay changeset id
>> *
>> @@ -913,7 +913,7 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>> */
>>
>> static int of_overlay_apply(const void *fdt, struct device_node *tree,
>> - int *ovcs_id)
>> + int *ovcs_id)
>> {
>> struct overlay_changeset *ovcs;
>> int ret = 0, ret_revert, ret_tmp;
>> @@ -953,7 +953,9 @@ 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. The aligned fdt
>> + * is contained within the memory at ovcs->fdt, possibly at an offset
>> + * from ovcs->fdt.
>> */
>> ret = overlay_notify(ovcs, OF_OVERLAY_PRE_APPLY);
>> if (ret) {
>> @@ -1014,9 +1016,10 @@ 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;
>> + u32 size, size_alloc;
>> struct device_node *overlay_root;
>>
>> *ovcs_id = 0;
>> @@ -1036,11 +1039,15 @@ 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_alloc = size + FDT_ALIGN_SIZE;
>> + new_fdt = kmalloc(size_alloc, GFP_KERNEL);
>
> As size_alloc is only used once, you can just do:
>
> new_fdt = kmalloc(size + FDT_ALIGN_SIZE, GFP_KERNEL);
>
> Same for the unittest. I can fix up.
>
> Applying now so this gets into linux-next this week.
Thanks, that change looks like an improvement to me.
>
> Rob
>