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

[Baoquan He]

On 05/16/17 at 08:56am, Dou Liyang wrote:
> 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.

No, could you tell why you want to add both "memmap=nnKMG" and "mem=" at
the same time? As you sid, what if I add "mem=4G mem=2G mem=1G"?

> 
> 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. */
> > 
> 
>