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Subject: Re: [PATCH] LoongArch: Add kernel address sanitizer support
To:     Xi Ruoyao <xry111@xry111.site>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Huacai Chen <chenhuacai@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        WANG Xuerui <kernel@xen0n.name>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        kasan-dev@googlegroups.com, linux-doc@vger.kernel.org,
        linux-mm@kvack.org, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
References: <20230328111714.2056-1-zhangqing@loongson.cn>
 <9817aaa043e9f0ed964bd523773447bd64f6e2c0.camel@xry111.site>
From:   Qing Zhang <zhangqing@loongson.cn>
Message-ID: <1c231587-3b70-22ab-d554-ebe3de407909@loongson.cn>
Date:   Tue, 28 Mar 2023 20:15:33 +0800
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Hi, Ruoyao

On 2023/3/28 下午7:39, Xi Ruoyao wrote:
> On Tue, 2023-03-28 at 19:17 +0800, Qing Zhang wrote:
> 
> /* snip */
> 
> 
>> -void * __init relocate_kernel(void)
>> +unsigned long __init relocate_kernel(void)
> 
> Why we must modify relocate_kernel for KASAN?

When the CONFIG_RANDOMIZE_BASE is enabled, the kernel will be updated to 
a random new address.
Kasan needs to call kasan_early_init before start_kernel.
There are two situations:
1> After enabling CONFIG_RELOCATABLE, call kasan_early_init.
2> After CONFIG_RELOCATABLE is not enabled, call kasan_early_init.

In order to prevent code redundancy and semantic problems caused by 
calling kasan_early_init (before jr a0) at the old PC.

Thanks,
-Qing
> 
>>   {
>>          unsigned long kernel_length;
>>          unsigned long random_offset = 0;
>>          void *location_new = _text; /* Default to original kernel start */
>> -       void *kernel_entry = start_kernel; /* Default to original kernel entry point */
>>          char *cmdline = early_ioremap(fw_arg1, COMMAND_LINE_SIZE); /* Boot command line is passed in fw_arg1 */
>>   
>>          strscpy(boot_command_line, cmdline, COMMAND_LINE_SIZE);
>> @@ -190,9 +189,6 @@ void * __init relocate_kernel(void)
>>   
>>                  reloc_offset += random_offset;
>>   
>> -               /* Return the new kernel's entry point */
>> -               kernel_entry = RELOCATED_KASLR(start_kernel);
>> -
>>                  /* The current thread is now within the relocated kernel */
>>                  __current_thread_info = RELOCATED_KASLR(__current_thread_info);
>>   
>> @@ -204,7 +200,7 @@ void * __init relocate_kernel(void)
>>   
>>          relocate_absolute(random_offset);
>>   
>> -       return kernel_entry;
>> +       return random_offset;
>