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

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Date:	Wed, 01 Jul 2015 15:13:29 +0300
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Andrey Konovalov <adech.fo@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Alexander Popov <alpopov@...ecurity.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/5] x86_64: fix kasan shadow region page tables

On 07/01/2015 12:07 PM, Ingo Molnar wrote:
> 
> * Andrey Ryabinin <a.ryabinin@...sung.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?


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