Re: [PATCH v5 2/3] KASLR: Handle memory limit specified by memmap and mem option

[Dou Liyang]

Hi Baoquan,

At 05/13/2017 01:46 PM, Baoquan He wrote:
> Option mem= will limit the max address a system can use and any memory
> region above the limit will be removed.
>
> Furthermore, memmap=nn[KMG] which has no offset specified has the same
> behaviour as mem=.
>
> KASLR needs to consider this when choosing the random position for
> decompressing the kernel. Do it now.
>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/kaslr.c | 68 +++++++++++++++++++++++++++++-----------
>  1 file changed, 50 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 106e13b..e0eba12 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -88,6 +88,10 @@ struct mem_vector {
>  static bool memmap_too_large;
>
>
> +/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
> +unsigned long long mem_limit = ULLONG_MAX;
> +
> +
>  enum mem_avoid_index {
>  	MEM_AVOID_ZO_RANGE = 0,
>  	MEM_AVOID_INITRD,
> @@ -138,16 +142,23 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>  		return -EINVAL;
>
>  	switch (*p) {
> -	case '@':
> -		/* Skip this region, usable */
> -		*start = 0;
> -		*size = 0;
> -		return 0;
>  	case '#':
>  	case '$':
>  	case '!':
>  		*start = memparse(p + 1, &p);
>  		return 0;
> +	case '@':
> +		/* memmap=nn@ss specifies usable region, should be skipped */
> +		*size = 0;
> +		/* Fall through */
> +	default:
> +		/*
> +		 * If w/o offset, only size specified, memmap=nn[KMG] has the
> +		 * same behaviour as mem=nn[KMG]. It limits the max address
> +		 * system can use. Region above the limit should be avoided.
> +		 */
> +		*start = 0;
> +		return 0;
>  	}
>
>  	return -EINVAL;
> @@ -173,9 +184,14 @@ static void mem_avoid_memmap(char *str)
>  		if (rc < 0)
>  			break;
>  		str = k;
> -		/* A usable region that should not be skipped */
> -		if (size == 0)
> +
> +		if (start == 0) {
> +			/* Store the specified memory limit if size > 0 */
> +			if (size > 0)
> +				mem_limit = size;

Baoquan,

I am not sure about setting the value of mem_limit to mem_size directly.

If the command line has both the "memmap" and "mem", such as
 ... mem=2G memmap=4G ...

...in that code, the mem_limit may be 4G not 2G.

In my opinion, How about following:

mem_limit = mem_limit > mem_size ? mem_size : mem_limit;

> +
>  			continue;
> +		}
>
>  		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
>  		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
> @@ -187,19 +203,15 @@ static void mem_avoid_memmap(char *str)
>  		memmap_too_large = true;
>  }
>
> -
> -/*
> - * handle_mem_memmap will also cover 'mem=' issue in next patch. Will remove
> - * this note later.
> - */
>  static int handle_mem_memmap(void)
>  {
>  	char *args = (char *)get_cmd_line_ptr();
>  	size_t len = strlen((char *)args);
>  	char *tmp_cmdline;
>  	char *param, *val;
> +	u64 mem_size;
>
> -	if (!strstr(args, "memmap="))
> +	if (!strstr(args, "memmap=") && !strstr(args, "mem="))
>  		return 0;
>
>  	tmp_cmdline = malloc(len + 1);
> @@ -222,8 +234,20 @@ static int handle_mem_memmap(void)
>  			return -1;
>  		}
>
> -		if (!strcmp(param, "memmap"))
> +		if (!strcmp(param, "memmap")) {
>  			mem_avoid_memmap(val);
> +		} else if (!strcmp(param, "mem")) {
> +			char *p = val;
> +
> +			if (!strcmp(p, "nopentium"))
> +				continue;
> +			mem_size = memparse(p, &p);
> +			if (mem_size == 0) {
> +				free(tmp_cmdline);
> +				return -EINVAL;
> +			}
> +			mem_limit = mem_size;

The same as above.

Thanks,
	Liyang.

> +		}
>  	}
>
>  	free(tmp_cmdline);
> @@ -460,7 +484,8 @@ static void process_e820_entry(struct boot_e820_entry *entry,
>  {
>  	struct mem_vector region, overlap;
>  	struct slot_area slot_area;
> -	unsigned long start_orig;
> +	unsigned long start_orig, end;
> +	struct boot_e820_entry cur_entry;
>
>  	/* Skip non-RAM entries. */
>  	if (entry->type != E820_TYPE_RAM)
> @@ -474,8 +499,15 @@ static void process_e820_entry(struct boot_e820_entry *entry,
>  	if (entry->addr + entry->size < minimum)
>  		return;
>
> -	region.start = entry->addr;
> -	region.size = entry->size;
> +	/* Ignore entries above memory limit */
> +	end = min(entry->size + entry->addr, mem_limit);
> +	if (entry->addr >= end)
> +		return;
> +	cur_entry.addr = entry->addr;
> +	cur_entry.size = end - entry->addr;
> +
> +	region.start = cur_entry.addr;
> +	region.size = cur_entry.size;
>
>  	/* Give up if slot area array is full. */
>  	while (slot_area_index < MAX_SLOT_AREA) {
> @@ -489,7 +521,7 @@ static void process_e820_entry(struct boot_e820_entry *entry,
>  		region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
>
>  		/* Did we raise the address above this e820 region? */
> -		if (region.start > entry->addr + entry->size)
> +		if (region.start > cur_entry.addr + cur_entry.size)
>  			return;
>
>  		/* Reduce size by any delta from the original address. */