[PATCH 3/4] KASLR: Handle memory limit specified by memmap and mem option

Baoquan He
2017-04-17T13:35:59Z

Option mem= will limit the max address system can use. Any memory
region above the limit will be removed. And memmap=nn[KMG] which
has no offset specified has the same behaviour as mem=. KASLR need
consider this when choose the random position for decompressing
kernel. Do it in this patch.

Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
---
arch/x86/boot/compressed/kaslr.c | 53 +++++++++++++++++++++++++++++++---------
1 file changed, 42 insertions(+), 11 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 36ab429..5361abd 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -67,6 +67,10 @@ int mem_avoid_memmap_index;
extern unsigned long get_cmd_line_ptr(void);

+/* 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,
@@ -117,15 +121,18 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
return -EINVAL;

switch (*p) {
- case '@':
- /* Skip this region, usable */
- *size = 0;
- *start = 0;
case '#':
case '$':
case '!':
*start = memparse(p + 1, &p);
return 0;
+ case '@':
+ /* Skip this region, usable */
+ *size = 0;
+ default:
+ /* Avoid the region which is above the amount limit */
+ *start = 0;
+ return 0;
}

return -EINVAL;
@@ -151,9 +158,14 @@ 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;
+
continue;
+ }

mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
@@ -173,6 +185,7 @@ static int handle_mem_memmap(void)
char tmp_cmdline[COMMAND_LINE_SIZE];
size_t len = strlen((char *)args);
char *param, *val;
+ u64 mem_size;

len = (len >= COMMAND_LINE_SIZE) ? COMMAND_LINE_SIZE - 1 : len;
memcpy(tmp_cmdline, args, len);
@@ -195,8 +208,18 @@ 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)
+ return -EINVAL;
+ mem_limit = mem_size;
+ }
}

return 0;
@@ -432,7 +455,8 @@ static void process_e820_entry(struct e820entry *entry,
{
struct mem_vector region, overlap;
struct slot_area slot_area;
- unsigned long start_orig;
+ unsigned long start_orig, end;
+ struct e820entry cur_entry;

/* Skip non-RAM entries. */
if (entry->type != E820_RAM)
@@ -446,8 +470,15 @@ static void process_e820_entry(struct e820entry *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 - 1, mem_limit);
+ if (entry->addr >= end)
+ return;
+ cur_entry.addr = entry->addr;
+ cur_entry.size = end - entry->addr + 1;
+
+ 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) {
@@ -461,7 +492,7 @@ static void process_e820_entry(struct e820entry *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. */
--
2.5.5