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Subject: Re: [PATCH v2 2/2] MIPS: Loongson64: Add KASLR support
To:     Jinyang He <hejinyang@loongson.cn>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhc@lemote.com>
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1606298866-7086-1-git-send-email-hejinyang@loongson.cn>
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-ID: <d6e07fad-da7d-065a-3b81-63b4f57f8fc0@flygoat.com>
Date:   Thu, 3 Dec 2020 12:05:10 +0800
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?? 2020/11/25 ????6:07, Jinyang He д??:
> Provide a weak plat_get_fdt() in relocate.c in case some platform enable
> USE_OF while plat_get_fdt() is useless.
>
> 1MB RELOCATION_TABLE_SIZE is small for Loongson64 because too many
> instructions should be relocated. 2MB is enough in present.
>
> Add KASLR support for Loongson64.
>
> KASLR(kernel address space layout randomization)
>
> To enable KASLR on Loongson64:
> First, make loongson3_defconfig.
> Then, enable CONFIG_RELOCATABLE and CONFIG_RANDOMIZE_BASE.
> Finally, compile the kernel.
>
> To test KASLR on Loongson64:
> Start machine with KASLR kernel.
>
> The first time:
> # cat /proc/iomem
> 00200000-0effffff : System RAM
>    02f30000-03895e9f : Kernel code
>    03895ea0-03bc7fff : Kernel data
>    03e30000-04f43f7f : Kernel bss
>
> The second time:
> # cat /proc/iomem
> 00200000-0effffff : System RAM
>    022f0000-02c55e9f : Kernel code
>    02c55ea0-02f87fff : Kernel data
>    031f0000-04303f7f : Kernel bss
>
> We see that code, data and bss sections become randomize.
>
> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
> ---
>
> v2:
> - Define weak plat_get_fdt() in relocate.c
> - Add default RELOCATION_TABLE_SIZE for Loongson64
>
>   arch/mips/Kconfig           | 5 ++++-
>   arch/mips/kernel/relocate.c | 7 +++++++
>   2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 0f638bf..44a47ad 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -488,6 +488,7 @@ config MACH_LOONGSON64
>   	select SYS_SUPPORTS_HIGHMEM
>   	select SYS_SUPPORTS_LITTLE_ENDIAN
>   	select SYS_SUPPORTS_ZBOOT
> +	select SYS_SUPPORTS_RELOCATABLE
>   	select ZONE_DMA32
>   	select NUMA
>   	select SMP
> @@ -2778,7 +2779,8 @@ config RELOCATABLE
>   	depends on CPU_MIPS32_R2 || CPU_MIPS64_R2 || \
>   		   CPU_MIPS32_R5 || CPU_MIPS64_R5 || \
>   		   CPU_MIPS32_R6 || CPU_MIPS64_R6 || \
> -		   CPU_P5600 || CAVIUM_OCTEON_SOC
> +		   CPU_P5600 || CAVIUM_OCTEON_SOC || \
> +		   CPU_LOONGSON64
>   	help
>   	  This builds a kernel image that retains relocation information
>   	  so it can be loaded someplace besides the default 1MB.
> @@ -2789,6 +2791,7 @@ config RELOCATION_TABLE_SIZE
>   	hex "Relocation table size"
>   	depends on RELOCATABLE
>   	range 0x0 0x01000000
> +	default "0x00200000" if CPU_LOONGSON64
>   	default "0x00100000"

Not relevant to the patch but how would we now if the reloc table is to 
small?
Is it possible to have a kind of checking script?

Thanks.

- Jiaxun

>   	help
>   	  A table of relocation data will be appended to the kernel binary
> diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
> index 8561c7a..57bdd276 100644
> --- a/arch/mips/kernel/relocate.c
> +++ b/arch/mips/kernel/relocate.c
> @@ -294,6 +294,13 @@ static inline int __init relocation_addr_valid(void *loc_new)
>   	return 1;
>   }
>   
> +#if defined(CONFIG_USE_OF)
> +void __weak *plat_get_fdt(void)
> +{
> +	return NULL;
> +}
> +#endif
> +
>   void *__init relocate_kernel(void)
>   {
>   	void *loc_new;