[PATCH 1/3] fdt: common API to populate kaslr seed
Sean Edmond
seanedmond at linux.microsoft.com
Mon Aug 14 21:12:41 CEST 2023
On 2023-08-12 6:09 a.m., Simon Glass wrote:
> Hi Sean,
>
> On Fri, 11 Aug 2023 at 11:14, Sean Edmond <seanedmond at linux.microsoft.com>
> wrote:
>>
>> On 2023-08-09 6:49 p.m., Simon Glass wrote:
>>> Hi Sean,
>>>
>>> On Wed, 9 Aug 2023 at 16:35, Sean Edmond <seanedmond at linux.microsoft.com>
> wrote:
>>>> On 2023-08-08 7:03 p.m., Simon Glass wrote:
>>>>> Hi,
>>>>>
>>>>> On Fri, 4 Aug 2023 at 17:34, <seanedmond at linux.microsoft.com> wrote:
>>>>>> From: Dhananjay Phadke <dphadke at linux.microsoft.com>
>>>>>>
>>>>>> fdt_fixup_kaslr_seed() will update given FDT with random seed value.
>>>>>> Source for random seed can be TPM or RNG driver in u-boot or sec
>>>>>> firmware (ARM).
>>>>>>
>>>>>> Signed-off-by: Dhananjay Phadke <dphadke at linux.microsoft.com>
>>>>>> ---
>>>>>> arch/arm/cpu/armv8/sec_firmware.c | 32
> +++++++------------------------
>>>>>> common/fdt_support.c | 31
> ++++++++++++++++++++++++++++++
>>>>>> include/fdt_support.h | 3 +++
>>>>>> 3 files changed, 41 insertions(+), 25 deletions(-)
>>>>> We need to find a way to use the ofnode API here.
>>>>>
>>>>>> diff --git a/arch/arm/cpu/armv8/sec_firmware.c
> b/arch/arm/cpu/armv8/sec_firmware.c
>>>>>> index c0e8726346..84ba49924e 100644
>>>>>> --- a/arch/arm/cpu/armv8/sec_firmware.c
>>>>>> +++ b/arch/arm/cpu/armv8/sec_firmware.c
>>>>>> @@ -411,46 +411,28 @@ int sec_firmware_init(const void
> *sec_firmware_img,
>>>>>> /*
>>>>>> * fdt_fix_kaslr - Add kalsr-seed node in Device tree
>>>>>> * @fdt: Device tree
>>>>>> - * @eret: 0 in case of error, 1 for success
>>>>>> + * @eret: 0 for success
>>>>>> */
>>>>>> int fdt_fixup_kaslr(void *fdt)
>>>>> You could pass an oftree to this function, e.g. obtained with:
>>>>>
>>>>> oftree_from_fdt(fdt)
>>>> The common API I added is fdt_fixup_kaslr_seed(), which was added to
>>>> "common/fdt_support.c".
>>>>
>>>> There are 3 callers:
>>>> sec_firmware_init()->fdt_fixup_kaslr_seed()
>>>> do_kaslr_seed()->fdt_fixup_kaslr_seed()
>>>> image_setup_libfdt()->fdt_tpm_kaslr_seed->fdt_fixup_kaslr_seed()
>>>>
>>>> I think the ask is to create a common API that uses the ofnode API.
> So,
>>>> instead of fdt_fixup_kaslr_seed() I can create
>>>> ofnode_fixup_kaslr_seed()? Where should it live?
>>> If you like you could add common/ofnode_support.c ?
>>>
>>> But it is OK to have it in the same file, I think.
>>>
>>>> Are you also wanting
>>>> the callers (eg. fdt_tpm_kaslr_seed, fdt_fixup_kaslr) to take oftree as
>>>> input too?
>>> So far as you can go, yes. Also you may want to pass an ofnode (the
>>> root node) so that things can deal with adding their stuff to any
>>> node.
>>>
>>> Regards,
>>> Simon
>>
>> I re-worked the API to use the ofnode API and tested it on our board. I
>> was required to explicitly enable CONFIG_OFNODE_MULTI_TREE in order for
>> it to work.
>>
>> I have concerns this will create a breaking change for users of the
>> kaslr fdt touch up. In our case, if CONFIG_OFNODE_MULTI_TREE isn't set,
>> the control FDT gets touched up, not the kernel FDT as required.
>> Everything runs to completion, but "/proc/device-tree/chosen/kaslr-seed"
>> isn't present after boot.
>>
>> Am I missing something? Perhaps there's a way to modify the default
>> value for CONFIG_OFNODE_MULTI_TREE to ensure this works out-of-the-box?
>>
> Yes, perhaps we should enable this when fixups are used? Is there a way to
> tell?
I don't think there's a way to tell unfortunately. Fixups are always
called if OF_LIBFDT is enabled, and if an FDT is found during bootm.
I'm having trouble understanding the intention of the current default
for OFNODE_MULTI_TREE:
default y if EVENT && !DM_DEV_READ_INLINE && !DM_INLINE_OFNODE
Could we simplify to this?
default y if !OF_LIVE
>
> Also, we should make it return an error when attempting to use a tree
> without that option enabled. I would expect oftree_ensure() to provide that?
I'll add a check.
>
> Regards,
> Simon
>
>
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