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Subject: Re: [PATCH] LoongArch: Add kernel address sanitizer support
To:     Huacai Chen <chenhuacai@kernel.org>
Cc:     Xi Ruoyao <xry111@xry111.site>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        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>
 <1c231587-3b70-22ab-d554-ebe3de407909@loongson.cn>
 <CAAhV-H5APsBxC8nNa81t3HXum1EU1hOj4S6UC7xLHD7_BCJd7g@mail.gmail.com>
From:   Qing Zhang <zhangqing@loongson.cn>
Message-ID: <9a6f11a3-d01c-e0c9-a4f3-47db25ce02f3@loongson.cn>
Date:   Wed, 29 Mar 2023 10:01:59 +0800
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Hi, Huacai

On 2023/3/29 上午8:22, Huacai Chen wrote:
> On Tue, Mar 28, 2023 at 8:15 PM Qing Zhang <zhangqing@loongson.cn> wrote:
>>
>> 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.
> In my opinion, you can call kasan_early_init before relocate_kernel in
> head.S, then no redundancy.
> 
It has no effect now, but kasan_early_init generally maps everything to
a single page of zeroes in kasan area, if placed
Before relocate_kernel, when the kernel was relocated, I worried that
there were changes other than the memory layout.

Thanks,
- Qing
> Huacai
>>
>> 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;
>>>
>>