Re: [PATCH] LoongArch: Add kernel address sanitizer support

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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@xxxxxxxxxxx> 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;







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