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SubjectRe: [PATCH v3 3/6] powerpc/fsl_booke/64: implement KASLR for fsl_booke64
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在 2020/3/5 5:44, Scott Wood 写道:
> On Thu, 2020-02-06 at 10:58 +0800, Jason Yan wrote:
>> The implementation for Freescale BookE64 is similar as BookE32. One
>> difference is that Freescale BookE64 set up a TLB mapping of 1G during
>> booting. Another difference is that ppc64 needs the kernel to be
>> 64K-aligned. So we can randomize the kernel in this 1G mapping and make
>> it 64K-aligned. This can save some code to creat another TLB map at
>> early boot. The disadvantage is that we only have about 1G/64K = 16384
>> slots to put the kernel in.
>>
>> To support secondary cpu boot up, a variable __kaslr_offset was added in
>> first_256B section. This can help secondary cpu get the kaslr offset
>> before the 1:1 mapping has been setup.
>
> What specifically requires __kaslr_offset instead of using kernstart_virt_addr
> like 32-bit does?
>

kernstart_virt_addr is in the data section. At the early boot we only
have a 64M tlb mapping. For the 32-bit I limited the kernel in a
64M-aligned region so that we can always get kernstart_virt_addr. But
for the 64-bit the kernel is bigger and not suitable to limit it in a
64M-aligned region.

So if we use kernstart_virt_addr and the kernel is randomized like below
, the secondary cpus will not boot up:

+------------+------------+
| 64M | 64M |
+------------+------------+
^ ^
| kernel |
^
kernstart_virt_addr

So I have to put the kernel offset in the first 64K along with the init
text.

>>
>> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
>> index ad79fddb974d..744624140fb8 100644
>> --- a/arch/powerpc/kernel/head_64.S
>> +++ b/arch/powerpc/kernel/head_64.S
>> @@ -104,6 +104,13 @@ __secondary_hold_acknowledge:
>> .8byte 0x0
>>
>> #ifdef CONFIG_RELOCATABLE
>> +#ifdef CONFIG_RANDOMIZE_BASE
>> + . = 0x58
>> + .globl __kaslr_offset
>> +__kaslr_offset:
>> +DEFINE_FIXED_SYMBOL(__kaslr_offset)
>> + .long 0
>> +#endif
>> /* This flag is set to 1 by a loader if the kernel should run
>> * at the loaded address instead of the linked address. This
>> * is used by kexec-tools to keep the the kdump kernel in the
>
> Why does it need to go here at a fixed address?
>

It does not need to be at a fixed address. I just want to keep
consistent and stay along with __run_at_load.

>
>>
>> /* check for a reserved-memory node and record its cell sizes */
>> regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory");
>> @@ -363,6 +374,17 @@ notrace void __init kaslr_early_init(void *dt_ptr,
>> phys_addr_t size)
>> unsigned long offset;
>> unsigned long kernel_sz;
>>
>> +#ifdef CONFIG_PPC64
>> + unsigned int *__kaslr_offset = (unsigned int *)(KERNELBASE + 0x58);
>> + unsigned int *__run_at_load = (unsigned int *)(KERNELBASE + 0x5c);
>
> Why are you referencing these by magic offset rather than by symbol?
>

I'm not sure if relocat works for fixed symbols. I will have a test and
swith to reference them by symbols if it works fine.

>
>> + /* Setup flat device-tree pointer */
>> + initial_boot_params = dt_ptr;
>> +#endif
>
> Why does 64-bit need this but 32-bit doesn't?

32-bit called early_get_first_memblock_info() very early which
implicitly setup the device-tree pointer.

>
> -Scott
>
>
>
> .
>

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