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

Chao Fan
2018-11-12T09:46:45Z

KASLR may randomly chooses some positions which are located in movable
memory regions. This will break memory hotplug feature and make the
movable memory chosen by KASLR can't be removed.

The solution is limite KASLR to choose memory regions in immovable
node according to SRAT tables.

If CONFIG_MEMORY_HOTREMOVE enabled, walk through the SRAT memory
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.

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
+

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,
+ 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.
+ */
+ if (num_immovable_mem == 0) {
+ 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;
+ }
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+ /*
+ * If immovable memory found, filter the intersection between
+ * immovable memory and region to slots_count.
+ * Otherwise, go on old code.
+ */
+ for (i = 0; i < num_immovable_mem; i++) {
+ struct mem_vector entry;
+ unsigned long long start, end, entry_end, region_end;
+
+ 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;
+
+ slots_count(&entry, 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;
+#endif
+}
+
#ifdef CONFIG_EFI
/*
* Returns true if mirror region found (and must have been processed
@@ -711,11 +772,8 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)

region.start = md->phys_addr;
region.size = md->num_pages << EFI_PAGE_SHIFT;
- process_mem_region(&region, minimum, image_size);
- if (slot_area_index == MAX_SLOT_AREA) {
- debug_putstr("Aborted EFI scan (slot_areas full)!\n");
+ if (process_mem_region(&region, minimum, image_size))
break;
- }
}
return true;
}
@@ -742,11 +800,8 @@ static void process_e820_entries(unsigned long minimum,
continue;
region.start = entry->addr;
region.size = entry->size;
- process_mem_region(&region, minimum, image_size);
- if (slot_area_index == MAX_SLOT_AREA) {
- debug_putstr("Aborted e820 scan (slot_areas full)!\n");
+ if (process_mem_region(&region, minimum, image_size))
break;
- }
}
}

--
2.19.1