linux-kernel - Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the immovable memory

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Date:   Mon, 27 Aug 2018 13:56:07 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, n-horiguchi@...jp.nec.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com,
        douly.fnst@...fujitsu.com
Subject: Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the
 immovable memory

On 08/07/18 at 02:50pm, Chao Fan wrote:
> If 'CONFIG_MEMORY_HOTREMOVE' specified and the account of immovable
If CONFIG_MEMORY_HOTREMOVE is enabled, 
> memory regions is not zero. Calculate the intersection between memory
> regions from e820/efi memory table and immovable memory regions.
> Or go on the old code.
> 
> Rename process_mem_region to slots_count to match slots_fetch_random,
> and name new function as process_mem_region.
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/kaslr.c | 66 ++++++++++++++++++++++++++------
>  1 file changed, 55 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 720878f967a3..9c6e24a23a2d 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -635,9 +635,9 @@ static unsigned long slots_fetch_random(void)
>  	return 0;
>  }
>  
> -static void process_mem_region(struct mem_vector *entry,
> -			       unsigned long minimum,
> -			       unsigned long image_size)
> +static void slots_count(struct mem_vector *entry,
> +			unsigned long minimum,
> +			unsigned long image_size)
>  {
>  	struct mem_vector region, overlap;
>  	struct slot_area slot_area;
> @@ -714,6 +714,56 @@ static void process_mem_region(struct mem_vector *entry,
>  	}
>  }
>  
> +static bool process_mem_region(struct mem_vector *region,
> +			       unsigned long long minimum,
> +			       unsigned long long image_size)
> +{

Is it possible to take num_immovable_mem definition out from #ifdef
CONFIG_MEMORY_HOTREMOVE block and check it here like below? This way,
one level of indentation can be reduced in the for loop, and code is
more readable.


static bool process_mem_region(struct mem_vector *region,
			       unsigned long long minimum,
			       unsigned long long image_size)
{

	/*
	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
	 * walk all the regions, so use region directely.
	 */
	if (num_immovable_mem > 0) {
		slots_count(region, minimum, image_size);
		
		if (slot_area_index == MAX_SLOT_AREA) {
			debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
			return 1;
		}
		return 0;
	}

#ifdef CONFIG_MEMORY_HOTREMOVE
	for (i = 0; i < num_immovable_mem; i++) {
		...
	}
#endif
}

> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +	/*
> +	 * If immovable memory found, filter the intersection between
> +	 * immovable memory and region to slots_count.
> +	 * Otherwise, go on old code.
> +	 */
> +	if (num_immovable_mem > 0) {
> +		int i;
> +
> +		for (i = 0; i < num_immovable_mem; i++) {
> +			struct mem_vector entry;
> +			unsigned long long start, end, entry_end, region_end;
> +
> +			start = immovable_mem[i].start;
> +			end = start + immovable_mem[i].size;
> +			region_end = region->start + region->size;
> +
> +			entry.start = clamp(region->start, start, end);
> +			entry_end = clamp(region_end, start, end);
> +
> +			if (entry.start + image_size < entry_end) {
> +				entry.size = entry_end - entry.start;
> +				slots_count(&entry, minimum, image_size);
> +
> +				if (slot_area_index == MAX_SLOT_AREA) {
> +					debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
> +					return 1;
> +				}
> +			}
> +		}
> +		return 0;
> +	}
> +#endif
> +	/*
> +	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
> +	 * walk all the regions, so use region directely.
> +	 */
> +	slots_count(region, minimum, image_size);
> +
> +	if (slot_area_index == MAX_SLOT_AREA) {
> +		debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
> +		return 1;
> +	}
> +	return 0;
> +}
> +
>  #ifdef CONFIG_EFI
>  /*
>   * Returns true if mirror region found (and must have been processed
> @@ -779,11 +829,8 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
>  
>  		region.start = md->phys_addr;
>  		region.size = md->num_pages << EFI_PAGE_SHIFT;
> -		process_mem_region(&region, minimum, image_size);
> -		if (slot_area_index == MAX_SLOT_AREA) {
> -			debug_putstr("Aborted EFI scan (slot_areas full)!\n");
> +		if (process_mem_region(&region, minimum, image_size))
>  			break;
> -		}
>  	}
>  	return true;
>  }
> @@ -810,11 +857,8 @@ static void process_e820_entries(unsigned long minimum,
>  			continue;
>  		region.start = entry->addr;
>  		region.size = entry->size;
> -		process_mem_region(&region, minimum, image_size);
> -		if (slot_area_index == MAX_SLOT_AREA) {
> -			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
> +		if (process_mem_region(&region, minimum, image_size))
>  			break;
> -		}
>  	}
>  }
>  
> -- 
> 2.17.1
> 
> 
>