[PATCH v9 1/5] x86/KASLR: Add kaslr_boot_mem=nn[KMG]@ss[KMG]

Chao Fan
2018-02-28T10:51:43Z

Introduce a new kernel parameter kaslr_boot_mem=nn[KMG]@ss[KMG] which is
used by KASLR only during kernel decompression stage.

Users can use it to specify memory regions where kernel can be randomized
into. E.g if movable_node specified in kernel cmdline, kernel could be
extracted into those movable regions, this will make memory hotplug fail.
With the help of 'kaslr_boot_mem=', limit kernel in those immovable regions
specified.

Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
Tested-by: Luiz Capitulino <lcapitulino@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
arch/x86/boot/compressed/kaslr.c | 73 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 70 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 66e42a098d70..e33e5cbf7244 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -114,6 +114,15 @@ enum mem_avoid_index {

static struct mem_vector mem_avoid[MEM_AVOID_MAX];

+/* Only support at most 4 usable memory regions specified for kaslr */
+#define MAX_KASLR_MEM_USABLE 4
+
+/* Store the usable memory regions for kaslr */
+static struct mem_vector mem_usable[MAX_KASLR_MEM_USABLE];
+
+/* The amount of usable regions for kaslr user specify, not more than 4 */
+static int num_usable_region;
+
static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
{
/* Item one is entirely before item two. */
@@ -212,7 +221,62 @@ static void mem_avoid_memmap(char *str)
memmap_too_large = true;
}

-static int handle_mem_memmap(void)
+static int parse_kaslr_boot_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;
+
+ switch (*p) {
+ case '@':
+ *start = memparse(p + 1, &p);
+ return 0;
+ default:
+ /*
+ * If w/o offset, only size specified, kaslr_boot_mem=nn[KMG]
+ * has the same behaviour as kaslr_boot_mem=nn[KMG]@0. It means
+ * the region starts from 0.
+ */
+ *start = 0;
+ return 0;
+ }
+
+ return -EINVAL;
+}
+
+static void parse_kaslr_boot_mem_regions(char *str)
+{
+ static int i;
+
+ while (str && (i < MAX_KASLR_MEM_USABLE)) {
+ int rc;
+ unsigned long long start, size;
+ char *k = strchr(str, ',');
+
+ if (k)
+ *k++ = 0;
+
+ rc = parse_kaslr_boot_mem(str, &start, &size);
+ if (rc < 0)
+ break;
+ str = k;
+
+ mem_usable[i].start = start;
+ mem_usable[i].size = size;
+ i++;
+ }
+ num_usable_region = i;
+}
+
+static int handle_mem_filter(void)
{
char *args = (char *)get_cmd_line_ptr();
size_t len = strlen((char *)args);
@@ -220,7 +284,8 @@ 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, "kaslr_boot_mem="))
return 0;

tmp_cmdline = malloc(len + 1);
@@ -245,6 +310,8 @@ static int handle_mem_memmap(void)

if (!strcmp(param, "memmap")) {
mem_avoid_memmap(val);
+ } else if (!strcmp(param, "kaslr_boot_mem")) {
+ parse_kaslr_boot_mem_regions(val);
} else if (!strcmp(param, "mem")) {
char *p = val;

@@ -384,7 +451,7 @@ 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