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SubjectRe: [PATCH v3 3/6] powerpc/fsl_booke/64: implement KASLR for fsl_booke64
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?

>
> 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?


>
> /* 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?


> + /* Setup flat device-tree pointer */
> + initial_boot_params = dt_ptr;
> +#endif

Why does 64-bit need this but 32-bit doesn't?

-Scott


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