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

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Date:	Mon, 25 May 2015 16:43:06 +0300
From:	Alexander Popov <alpopov@...ecurity.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	"Denys Vlasenko" <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Sergey Kovalev <SKovalev@...ecurity.com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86_64: fix KASan shadow region page tables

On 25.05.2015 11:12, Andrey Ryabinin wrote:
> On 05/22/2015 07:03 PM, Alexander Popov wrote:
>> Physical addresses in KASan shadow region page tables need fixup:
>> kernel halts without it if phys_base is not zero.
>>
> 
> Indeed.
> Since we have to patch page tables anyway, compile-time created kasan
> page tables become pointless.
> So, I'd suggest to create them in runtime. This could be done in plain C
> in kasan_map_early_shadow().
> 

Thanks for your reply, Andrey.

Creating kasan_zero_pud, kasan_zero_pmd and kasan_zero_pte in
kasan_map_early_shadow() doesn't look handy for me because this function
is called twice in x86_64_start_kernel().

What do you think about leaving the initialization of KASan shadow region
page tables in arch/x86/kernel/head_64.S and calling something like
kasan_fixup_early_shadow() before calling kasan_map_early_shadow()
for the first time?

Best regards,
Alexander

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