[PATCH] powerpc/boot: Fix the initrd being overwritten under qemu

[Alexey Kardashevskiy]

On 24/10/2019 12:31, Alexey Kardashevskiy wrote:
> 
> 
> On 23/10/2019 22:21, Segher Boessenkool wrote:
>> On Wed, Oct 23, 2019 at 12:36:35PM +1100, Oliver O'Halloran wrote:
>>> When booting under OF the zImage expects the initrd address and size to be
>>> passed to it using registers r3 and r4. SLOF (guest firmware used by QEMU)
>>> currently doesn't do this so the zImage is not aware of the initrd
>>> location.  This can result in initrd corruption either though the zImage
>>> extracting the vmlinux over the initrd, or by the vmlinux overwriting the
>>> initrd when relocating itself.
>>>
>>> QEMU does put the linux,initrd-start and linux,initrd-end properties into
>>> the devicetree to vmlinux to find the initrd. We can work around the SLOF
>>> bug by also looking those properties in the zImage.
>>
>> This is not a bug.  What boot protocol requires passing the initrd start
>> and size in GPR3, GPR4?
> 
> So far I was unable to identify it...
> 
>> The CHRP binding (what SLOF implements) requires passing two zeroes here.
>> And ePAPR requires passing the address of a device tree and a zero, plus
>> something in GPR6 to allow distinguishing what it does.
>>
>> As Alexey says, initramfs works just fine, so please use that?  initrd was
>> deprecated when this code was written already.
> 
> I did not say about anything working fine :)
> 
> In my case I was using a new QEMU which does full FDT on client-arch-support and that thing would put the original
> linux,initrd-start/end to the FDT even though the initrd was unpacked and the properties were changes in SLOF. With that
> fixed, this is an alternative fix for SLOF but I am not pushing it out as I have no idea about the bindings and this
> also breaks "vmlinux".


ah no, that works for vmlinux as well. Hm.


> 
> 
> diff --git a/slof/fs/client.fs b/slof/fs/client.fs
> index 8a7f6ac4326d..138177e4c2a3 100644
> --- a/slof/fs/client.fs
> +++ b/slof/fs/client.fs
> @@ -45,6 +45,17 @@ VARIABLE  client-callback \ Address of client's callback function
>    >r  ciregs >r7 !  ciregs >r6 !  client-entry-point @ ciregs >r5 !
>    \ Initialise client-stack-pointer
>    cistack ciregs >r1 !
> +
> +  s" linux,initrd-end" get-chosen IF decode-int -rot 2drop ELSE 0 THEN
> +  s" linux,initrd-start" get-chosen IF decode-int -rot 2drop ELSE 0 THEN
> +  2dup - dup IF
> +    ciregs >r4 !
> +    ciregs >r3 !
> +    drop
> +  ELSE
> +    3drop
> +  THEN
> +
> 
> 

-- 
Alexey