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

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Message-ID: <20150701090740.GA16645@gmail.com>
Date:	Wed, 1 Jul 2015 11:07:40 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
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


* 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.

That way if anything breaks in the generic code due to this change we have a 
simple commit to bisect to.

Thanks,

	Ingo
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