Re: [PATCH v2] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

[Dave Young]

Hi Chao,
On 04/04/19 at 03:20pm, Chao Fan wrote:
> On Thu, Apr 04, 2019 at 02:41:30PM +0800, Dave Young wrote:
> >On 04/04/19 at 11:22am, Dave Young wrote:
> >> On 04/04/19 at 11:10am, Baoquan He wrote:
> >> > On 04/04/19 at 11:00am, Baoquan He wrote:
> >> > > On 04/04/19 at 10:52am, Dave Young wrote:
> >> > > > On 04/04/19 at 01:23am, Junichi Nomura wrote:
> >> >  +	/* Save RSDP address for later use. */
> >> >  +	boot_params->acpi_rsdp_addr = get_rsdp_addr();
> >> >  +
> >> >  +	error("Hang kernel for kexec debugging");
> >> > 
> >> > Sorry, here I means calling error() to hang kernel after calling
> >> > get_rsdp_addr().
> >> 
> >> Thanks, it did not hang, it always reset to firmware/grub boot menu.
> >> I'm pretty sure now the bug exists in get_rsdp_addr().
> >
> >static acpi_physical_address kexec_get_rsdp_addr(void)
> >{
> >...
> >        /* Get systab from boot params. */
> >        systab = (efi_system_table_64_t *) (ei->efi_systab | ((__u64)ei->efi_systab_hi << 32));
> >        if (!systab)
> >              error("EFI system table not found in kexec boot_params.");
> > 
> >...
> >  -> add error("hang me") here will have a hang
> >...
> >        return __efi_get_rsdp_addr((unsigned long)esd->tables,
> >                                   systab->nr_tables, true);
> > 
> 
> I have an idea, but not sure whether is a problem.
> In code of Nomura:
> 
> #if defined(CONFIG_EFI) && defined(CONFIG_X86_64)
> [...]
>         if (strncmp(sig, EFI64_LOADER_SIGNATURE, 4)) {
>                 debug_putstr("Wrong kexec EFI loader signature.\n");
>                 return 0;
>         }
> 
>         /* Get systab from boot params. */
>         systab = (efi_system_table_64_t *) (ei->efi_systab | ((__u64)ei->efi_systab_hi << 32));
> [...]
> #endif
> 
> After review agian, I wonder what will happen if 32bit-efi boot 64bit
> OS.

It is hard to find 32bit efi hardware, I can confirm all the laptop I
have are 64bit efi.

In case 32bit efi EFI64_LOADER_SIGNATURE checking will be false.