Re: [PATCH v11 5/5] x86/boot/KASLR: Walk srat tables to filter immovable memory

Chao Fan
2018-11-19T01:31:23Z

On Fri, Nov 16, 2018 at 02:50:39PM +0100, Borislav Petkov wrote:
> Subject: Re: [PATCH v11 5/5] x86/boot/KASLR: Walk srat tables to filter immovable memory
>
>s/srat/SRAT/g
>
>On Mon, Nov 12, 2018 at 05:46:45PM +0800, Chao Fan wrote:
>> KASLR may randomly chooses some positions which are located in movable
>
> choose
>
>> memory regions. This will break memory hotplug feature and make the
>> movable memory chosen by KASLR can't be removed.
>
> by KASLR practically immovable.

Thanks,

>
>:)
>
>> The solution is limite KASLR to choose memory regions in immovable
>
>limite?
>
>"to limit"
>
>> node according to SRAT tables.
>>
>> If CONFIG_MEMORY_HOTREMOVE enabled, walk through the SRAT memory
>
> *is* enabled,
>
>> tables and store those immovable memory regions so that KASLR can get
>> where to choose for randomization.
>>
>> If the amount of immovable memory regions is not zero, which
>> means the immovable memory regions existing. Calculate the intersection
>> between memory regions from e820/efi memory table and immovable memory
>> regions.
>
>This is explaining *what* the patch does and generally doesn't need to
>be in the commit messge as people can read it in the patch itself.

OK,

>
>> Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
>> ---
>> arch/x86/boot/compressed/kaslr.c | 77 +++++++++++++++++++++++++++-----
>> 1 file changed, 66 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>> index b251572e77af..174d2114045e 100644
>> --- a/arch/x86/boot/compressed/kaslr.c
>> +++ b/arch/x86/boot/compressed/kaslr.c
>> @@ -97,6 +97,11 @@ 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_MEMORY_HOTREMOVE
>> +/* Store the immovable memory regions */
>> +extern struct mem_vector immovable_mem[MAX_NUMNODES*2];
>> +#endif
>
>For this and the other occurrences of ifdef CONFIG_MEMORY_HOTREMOVE,
>define empty stubs for those functions in a header and remove the
>ifdeffery at the call sites.

OK,

>
>> +
>>
>> enum mem_avoid_index {
>> MEM_AVOID_ZO_RANGE = 0,
>> @@ -413,6 +418,11 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>> /* Mark the memmap regions we need to avoid */
>> handle_mem_options();
>>
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> + /* Mark the immovable regions we need to choose */
>> + get_immovable_mem();
>> +#endif
>> +
>> #ifdef CONFIG_X86_VERBOSE_BOOTUP
>> /* Make sure video RAM can be used. */
>> add_identity_map(0, PMD_SIZE);
>> @@ -568,9 +578,9 @@ 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 slots_count(struct mem_vector *entry,
>
>That's a strange rename.
>
I will change it.

Thanks,
Chao Fan

>__process_mem_region() makes more sense to me.
>
>> + unsigned long minimum,
>> + unsigned long image_size)
>> {
>> struct mem_vector region, overlap;
>> unsigned long start_orig, end;
>> @@ -646,6 +656,57 @@ 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 directely.
>
>"directly"
>
>> + */
>> + if (num_immovable_mem == 0) {
>
> if (!...
>
>> + slots_count(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;
>> + }
>> +
>
>--
>Regards/Gruss,
> Boris.
>
>Good mailing practices for 400: avoid top-posting and trim the reply.
>
>