[PATCH v3 4/4] arm64: Trap non-PIE builds early if starting from wrong address

[Michal Simek <michal.simek@xilinx.com>]

On 10. 09. 20 15:06, Andr? Przywara wrote:
> On 10/09/2020 13:38, Michal Simek wrote:
>>
>>
>> On 09. 09. 20 19:07, Edgar E. Iglesias wrote:
>>> From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
>>>
>>> Trap non-PIE builds early if the start address doesn't match
>>> between run-time and link-time. This will trap the startup
>>> sequence rather than letting it run into obscure errors.
>>>
>>> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
>>> ---
>>>  arch/arm/cpu/armv8/start.S | 13 +++++++++++++
>>>  1 file changed, 13 insertions(+)
>>>
>>> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
>>> index e5c2856cf5..39e1b842c4 100644
>>> --- a/arch/arm/cpu/armv8/start.S
>>> +++ b/arch/arm/cpu/armv8/start.S
>>> @@ -101,6 +101,19 @@ pie_skip_reloc:
>>>  	cmp	x2, x3
>>>  	b.lo	pie_fix_loop
>>>  pie_fixup_done:
>>> +#else
>>> +	adr	x0, _start
>>> +	ldr	x1, _TEXT_BASE
>>> +	cmp	x0, x1
>>> +	beq	1f
>>> +0:
>>> +	/*
>>> +	 * FATAL, can't continue.
>>> +	 * U-Boot needs to start executing at CONFIG_SYS_TEXT_BASE.
>>> +	 */
>>> +	wfi
>>> +	b	0b
>>> +1:
>>>  #endif
>>>  
>>>  #ifdef CONFIG_SYS_RESET_SCTRL
>>>
>>
>> NACK for this.
>>
>> 1. It breaks SPL flow because CONFIG_SYS_TEXT_BASE is text base for
>> U-Boot proper
>> 2. It likely also breaks TPL flow for the same reason
>>
>> 3. And last thing is that this code is used only for U-Boot proper.
>> .globl	_TEXT_BASE
>> _TEXT_BASE:
>> 	.quad	CONFIG_SYS_TEXT_BASE
>>
>> The fixes are below. Point 3 should be likely be in separate patch
>> because it is unrelated.
> 
> So if this patch causes issues, can't we just drop it? I mean right now
> you will probably just crash anyway if you load it at the wrong address,
> but maybe late enough that you get more hints or even some output.
> 
> Now this patch makes sure that you don't get anything, so I don't see
> how this is really improving the situation. It seems like a case of
> "don't fix things that ain't broken".

I am fine with dropping it.
Tom: What do you think?

Thanks,
Michal