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

Chao Fan
2019-01-17T01:26:58Z

On Wed, Jan 16, 2019 at 12:15:07PM +0100, Borislav Petkov wrote:
>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.
>

Will drop it.
>>
>> Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
>> ---
>> 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?
>

Will drop it.
>> +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.

Will make num_immovable_mem returned, and how do you think change
the function name as "get_immovable_mem_num()" since the function
will return num_immovable_mem.
>
>> +
>> #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.

Will change it.

Thanks,
Chao Fan

>
>--
>Regards/Gruss,
> Boris.
>
>Good mailing practices for 400: avoid top-posting and trim the reply.
>
>