Re: [PATCH v15 6/6] x86/boot/KASLR: Limit KASLR to extracting kernel in immovable memory

[Borislav Petkov]

On Mon, Jan 07, 2019 at 11:22:43AM +0800, Chao Fan wrote:
> KASLR may randomly choose some positions which are located in movable
> memory regions. It will break memory hotplug feature and make the
> movable memory chosen by KASLR can't be removed.
> 
> The solution is to limit KASLR to choose memory regions in immovable
> node according to SRAT tables.
> When CONFIG_EARLY_SRAT_PARSE is enabled, walk through SRAT to get the
> information of immovable memory so that KASLR knows where should be
> chosen for randomization.
> 
> Rename process_mem_region() as __process_mem_region() and name new
> function as process_mem_region().

The commit message doesn't need to contain *what* you're doing in the
patch.

> 
> Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/kaslr.c | 79 +++++++++++++++++++++++++++-----
>  1 file changed, 68 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index b251572e77af..7dbec6910203 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -97,6 +97,15 @@ static bool memmap_too_large;
>  /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
>  static unsigned long long mem_limit = ULLONG_MAX;
>  
> +#ifdef CONFIG_EARLY_SRAT_PARSE
> +/*
> + * Information of immovable memory regions.
> + * Max amount of memory regions is MAX_NUMNODES*2, so need such array
> + * to place immovable memory regions if all of the memory is immovable.
> + */

Why is that comment repeated here?

> +extern struct mem_vector immovable_mem[MAX_NUMNODES*2];
> +#endif
> +
>  
>  enum mem_avoid_index {
>  	MEM_AVOID_ZO_RANGE = 0,
> @@ -413,6 +422,9 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>  	/* Mark the memmap regions we need to avoid */
>  	handle_mem_options();
>  
> +	/* Mark the immovable regions we need to choose */
> +	get_immovable_mem();

get != mark.

Which should tell you that the function name needs changing.

Also, this function is void and it could very well return
num_immovable_mem and num_immovable_mem can be a static variable in
kaslr.c instead of sloppily adding yet another global one.

> +
>  #ifdef CONFIG_X86_VERBOSE_BOOTUP
>  	/* Make sure video RAM can be used. */
>  	add_identity_map(0, PMD_SIZE);
> @@ -568,9 +580,9 @@ 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 __process_mem_region(struct mem_vector *entry,
> +				 unsigned long minimum,
> +				 unsigned long image_size)
>  {
>  	struct mem_vector region, overlap;
>  	unsigned long start_orig, end;
> @@ -646,6 +658,57 @@ 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)
> +{
> +	int i;
> +	/*
> +	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
> +	 * walk all the regions, so use region directly.
> +	 */
> +	if (!num_immovable_mem) {
> +		__process_mem_region(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_EARLY_SRAT_PARSE
> +	/*
> +	 * If immovable memory found, filter the intersection between
> +	 * immovable memory and region to __process_mem_region().
> +	 * Otherwise, go on old code.
> +	 */
> +	for (i = 0; i < num_immovable_mem; i++) {
> +		unsigned long long start, end, entry_end, region_end;
> +		struct mem_vector entry;
> +
> +		if (!mem_overlaps(region, &immovable_mem[i]))
> +			continue;
> +
> +		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);
> +		entry.size = entry_end - entry.start;
> +
> +		__process_mem_region(&entry, minimum, image_size);
> +
> +		if (slot_area_index == MAX_SLOT_AREA) {
> +			debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");

Change this error message a bit to differ from the above for easier debugging.

-- 
Regards/Gruss,
    Boris.

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