Re: [PATCH v3 1/4] kaslr: add immovable_mem=nn[KMG]@ss[KMG] to specify extracting memory

[Chao Fan]

On Tue, Dec 05, 2017 at 11:42:42AM -0800, Kees Cook wrote:
>On Tue, Dec 5, 2017 at 12:51 AM, Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> wrote:
>> In current code, kaslr may choose the memory region in movable
>> nodes to extract kernel, which will make the nodes can't be hot-removed.
>> To solve it, we can specify the memory region in immovable node.
>> Create immovable_mem to store the regions in immovable_mem, where should
>> be chosen by kaslr.
>>
>> Multiple regions can be specified, comma delimited.
>> Considering the usage of memory, only support for 4 regions.
>> 4 regions contains 2 nodes at least, enough for kernel to extract.
>>
>> Also change the "handle_mem_memmap" to "handle_mem_filter", since
>> it will not only handle memmap parameter now.
>

Hi Kees,

Thanks for your reply.

>I would put all immovable region functions and variables behind
>#ifdefs. e.g. parse_immovable_mem() is unused without

Yes, you are right.

>CONFIG_MEMORY_HOTPLUG. I also wonder if it might be possible to reuse
>some of the parsing code and just pass in which array you're updating

I will try to change it in the next version.

Thanks,
Chao Fan

>(i.e. memmap array vs immovable array).
>



>-Kees
>
>>
>> Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
>> ---
>>  arch/x86/boot/compressed/kaslr.c | 80 ++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 77 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>> index a63fbc25ce84..0bbbaf5f6370 100644
>> --- a/arch/x86/boot/compressed/kaslr.c
>> +++ b/arch/x86/boot/compressed/kaslr.c
>> @@ -108,6 +108,15 @@ enum mem_avoid_index {
>>
>>  static struct mem_vector mem_avoid[MEM_AVOID_MAX];
>>
>> +/* Only supporting at most 4 immovable memory regions with kaslr */
>> +#define MAX_IMMOVABLE_MEM      4
>> +
>> +/* Store the memory regions in immovable node */
>> +static struct mem_vector immovable_mem[MAX_IMMOVABLE_MEM];
>> +
>> +/* The immovable regions user specify, not more than 4 */
>> +static int num_immovable_region;
>> +
>>  static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>>  {
>>         /* Item one is entirely before item two. */
>> @@ -168,6 +177,38 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>>         return -EINVAL;
>>  }
>>
>> +static int parse_immovable_mem(char *p,
>> +                              unsigned long long *start,
>> +                              unsigned long long *size)
>> +{
>> +       char *oldp;
>> +
>> +       if (!p)
>> +               return -EINVAL;
>> +
>> +       oldp = p;
>> +       *size = memparse(p, &p);
>> +       if (p == oldp)
>> +               return -EINVAL;
>> +
>> +       /* We support nn[KMG]@ss[KMG] and nn[KMG]. */
>> +       switch (*p) {
>> +       case '@':
>> +               *start = memparse(p + 1, &p);
>> +               return 0;
>> +       default:
>> +               /*
>> +                * If w/o offset, only size specified, immovable_mem=nn[KMG]
>> +                * has the same behaviour as immovable_mem=nn[KMG]@0. It means
>> +                * the region starts from 0.
>> +                */
>> +               *start = 0;
>> +               return 0;
>> +       }
>> +
>> +       return -EINVAL;
>> +}
>> +
>>  static void mem_avoid_memmap(char *str)
>>  {
>>         static int i;
>> @@ -207,7 +248,37 @@ static void mem_avoid_memmap(char *str)
>>                 memmap_too_large = true;
>>  }
>>
>> -static int handle_mem_memmap(void)
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static void parse_immovable_mem_regions(char *str)
>> +{
>> +       static int i;
>> +
>> +       while (str && (i < MAX_IMMOVABLE_MEM)) {
>> +               int rc;
>> +               unsigned long long start, size;
>> +               char *k = strchr(str, ',');
>> +
>> +               if (k)
>> +                       *k++ = 0;
>> +
>> +               rc = parse_immovable_mem(str, &start, &size);
>> +               if (rc < 0)
>> +                       break;
>> +               str = k;
>> +
>> +               immovable_mem[i].start = start;
>> +               immovable_mem[i].size = size;
>> +               i++;
>> +       }
>> +       num_immovable_region = i;
>> +}
>> +#else
>> +static inline void parse_immovable_mem_regions(char *str)
>> +{
>> +}
>> +#endif
>> +
>> +static int handle_mem_filter(void)
>>  {
>>         char *args = (char *)get_cmd_line_ptr();
>>         size_t len = strlen((char *)args);
>> @@ -215,7 +286,8 @@ static int handle_mem_memmap(void)
>>         char *param, *val;
>>         u64 mem_size;
>>
>> -       if (!strstr(args, "memmap=") && !strstr(args, "mem="))
>> +       if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
>> +           !strstr(args, "immovable_mem="))
>>                 return 0;
>>
>>         tmp_cmdline = malloc(len + 1);
>> @@ -240,6 +312,8 @@ static int handle_mem_memmap(void)
>>
>>                 if (!strcmp(param, "memmap")) {
>>                         mem_avoid_memmap(val);
>> +               } else if (!strcmp(param, "immovable_mem")) {
>> +                       parse_immovable_mem_regions(val);
>>                 } else if (!strcmp(param, "mem")) {
>>                         char *p = val;
>>
>> @@ -379,7 +453,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>>         /* We don't need to set a mapping for setup_data. */
>>
>>         /* Mark the memmap regions we need to avoid */
>> -       handle_mem_memmap();
>> +       handle_mem_filter();
>>
>>  #ifdef CONFIG_X86_VERBOSE_BOOTUP
>>         /* Make sure video RAM can be used. */
>> --
>> 2.14.3
>>
>>
>>
>
>
>
>-- 
>Kees Cook
>Pixel Security
>
>