Re: [PATCH] boot: Assure FDT is always at 8-byte aligned address

[Marek Vasut <marek.vasut@mailbox.org>]

On 11/13/25 8:33 PM, Simon Glass wrote:

Hello Simon,

>> The fitImage may contain FDT at 4-byte aligned address, because alignment
>> of DT tags is 4 bytes. However, libfdt and also Linux expects DT to be at
>> 8-byte aligned address. Make sure that the DTs embedded in fitImages are
>> always used from 8-byte aligned addresses. In case the DT is decompressed,
>> make sure the target buffer is 8-byte aligned. In case the DT is only
>> loaded, make sure the target buffer is 8-byte aligned too.
>>
>> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
>> ---
>> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
>> Cc: Quentin Schulz <quentin.schulz@cherry.de>
>> Cc: Simon Glass <sjg@chromium.org>
>> Cc: Tom Rini <trini@konsulko.com>
>> Cc: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
>> Cc: u-boot@lists.denx.de
>> ---
>>   boot/image-fit.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/boot/image-fit.c b/boot/image-fit.c
>> index 2f2d3e9304d..cccaa48f683 100644
>> --- a/boot/image-fit.c
>> +++ b/boot/image-fit.c
>> @@ -23,7 +23,6 @@
>>   #include <log.h>
>>   #include <mapmem.h>
>>   #include <asm/io.h>
>> -#include <malloc.h>
>>   #include <memalign.h>
>>   #include <asm/global_data.h>
>>   #ifdef CONFIG_DM_HASH
>> @@ -36,6 +35,7 @@ DECLARE_GLOBAL_DATA_PTR;
>>   #include <bootm.h>
>>   #include <image.h>
>>   #include <bootstage.h>
>> +#include <malloc.h>
>>   #include <upl.h>
>>   #include <u-boot/crc.h>
>>
>> @@ -2279,7 +2279,7 @@ int fit_image_load(struct bootm_headers *images, ulong addr,
>>
>>                  log_debug("decompressing image\n");
>>                  if (load == data) {
>> -                       loadbuf = malloc(max_decomp_len);
>> +                       loadbuf = memalign(8, max_decomp_len);
>>                          load = map_to_sysmem(loadbuf);
>>                  } else {
>>                          loadbuf = map_sysmem(load, max_decomp_len);
>> @@ -2291,6 +2291,11 @@ int fit_image_load(struct bootm_headers *images, ulong addr,
>>                          return -ENOEXEC;
>>                  }
>>                  len = load_end - load;
>> +       } else if (load_op != FIT_LOAD_IGNORED && image_type == IH_TYPE_FLATDT &&
>> +                  ((uintptr_t)buf & 7)) {
>> +               loadbuf = memalign(8, len);
>> +               load = map_to_sysmem(loadbuf);
>> +               memcpy(loadbuf, buf, len);
>>          } else if (load != data) {
>>                  log_debug("copying\n");
>>                  loadbuf = map_sysmem(load, len);
>> --
>> 2.51.0
>>
> 
> We really can't do a memory allocation in fit_image_load() !

We already do, notice the malloc() when "decompressing image" part.

> The problem should be fixed higher up, in its callers, etc. For one
> thing, the caller knows whether it is a DT or not, so putting this
> logic here is messy. See boot_get_fdt_fit()

This is triggered by a fitImage with DT embedded in that fitImage as 
non-external-data. That DT is at 4-byte aligned address, so how can the 
caller deal with it ? The caller gets a fitImage, which itself is at 
8-byte aligned address, but the DT in it is not at 8-byte aligned 
address, so that DT has to be relocated somehow and that happens here.