linux-kernel - Re: [PATCH v2 1/1] x86_64: fix KASan shadow region page tables

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Date:	Fri, 29 May 2015 17:51:10 +0300
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Alexander Popov <alpopov@...ecurity.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Borislav Petkov <bp@...e.de>,
	Denys Vlasenko <dvlasenk@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] x86_64: fix KASan shadow region page tables

On 05/29/2015 04:46 PM, Alexander Popov wrote:
> KASan shadow region page tables can't be filled statically because
> physical addresses in these page tables depend on phys_base.
> Initialize KASan shadow region page tables in kasan_early_init().
> 
> Signed-off-by: Alexander Popov <alpopov@...ecurity.com>
> ---

Thanks. Couple comments bellow, otherwise looks good.

>  
> -extern unsigned char kasan_zero_page[PAGE_SIZE];
> +static pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_data;
> +static pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_data;
> +static pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_data;

It's better to keep these in bss.


> +/*
> + * This page used as early shadow. We don't use empty_zero_page
> + * at early stages, stack instrumentation could write some garbage
> + * to this page.
> + * Latter we reuse it as zero shadow for large ranges of memory
> + * that allowed to access, but not instrumented by kasan
> + * (vmalloc/vmemmap ...).
> + */
> +static unsigned char kasan_zero_page[PAGE_SIZE] __page_aligned_bss;
>  
>  static int __init map_range(struct range *range)
>  {
> @@ -166,6 +178,23 @@ static struct notifier_block kasan_die_notifier = {
>  };
>  #endif
>  
> +void __init kasan_early_init(void)
> +{
> +	int i;
> +	pteval_t pte_val = __pa_nodebug(kasan_zero_page) | _KERNPG_TABLE;


Should be __PAGE_KERNEL.
Yes, currently kasan's ptes have _KERNPG_TABLE flags, but that is wrong.
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