Re: [PATCH 1/5] x86_64: fix kasan shadow region page tables

Andrey Ryabinin
2015-07-01T12:13:39Z

On 07/01/2015 12:07 PM, Ingo Molnar wrote:
>
> * Andrey Ryabinin <a.ryabinin@samsung.com> wrote:
>
>> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
>> index 5a46681..f129a9a 100644
>> --- a/arch/x86/kernel/head64.c
>> +++ b/arch/x86/kernel/head64.c
>> @@ -161,11 +161,12 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>> /* Kill off the identity-map trampoline */
>> reset_early_page_tables();
>>
>> - kasan_map_early_shadow(early_level4_pgt);
>> -
>> - /* clear bss before set_intr_gate with early_idt_handler */
>> clear_bss();
>>
>> + clear_page(init_level4_pgt);
>> +
>> + kasan_early_init();
>> +
>> for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
>> set_intr_gate(i, early_idt_handler_array[i]);
>> load_idt((const struct desc_ptr *)&idt_descr);
>> @@ -177,12 +178,9 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>> */
>> load_ucode_bsp();
>>
>> - clear_page(init_level4_pgt);
>> /* set init_level4_pgt kernel high mapping*/
>> init_level4_pgt[511] = early_level4_pgt[511];
>>
>> - kasan_map_early_shadow(init_level4_pgt);
>> -
>> x86_64_start_reservations(real_mode_data);
>> }
>>
>
> So this changes generic code (moves the clear_page(init_level4_pgt) call), but the
> changelog claims it's a KASAN-specific change.
>
> Please split this into two patches: the first one does the generic change, the
> second one the KASAN specific one.
>

Hm... We will need to backport that generic change to stable, because second change depends on it.
So, maybe split this on three changes:

#1 fix kasan page tables (without touching clear_page() or kasan_map_early_shadow(init_level4_pgt))
#2 generic move clear_page()
#3 clean up kasan initialization (move kasan_map_early_shadow(init_level4_pgt)).

Only #1 will have stable tag. Does that makes sense?