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

[Qing Zhang]

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;