Adding "kaslr-seed" to dtb enables triggering kaslr, or kernel virtual
address randomization, at secondary kernel boot. We always do this as
it will have no harm on kaslr-incapable kernel.
We don't have any "switch" to turn off this feature directly, but still
can suppress it by passing "nokaslr" as a kernel boot argument.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
---
arch/arm64/kernel/machine_kexec_file.c | 45 ++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index ecaecb122cad..967db9824e3f 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -16,6 +16,7 @@
#include <linux/libfdt.h>
#include <linux/memblock.h>
#include <linux/of_fdt.h>
+#include <linux/random.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
@@ -27,6 +28,7 @@
#define FDT_PSTR_INITRD_STA "linux,initrd-start"
#define FDT_PSTR_INITRD_END "linux,initrd-end"
#define FDT_PSTR_BOOTARGS "bootargs"
+#define FDT_PSTR_KASLR_SEED "kaslr-seed"
const struct kexec_file_ops * const kexec_file_loaders[] = {
&kexec_image_ops,
@@ -45,6 +47,32 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
return kexec_image_post_load_cleanup_default(image);
}
+/* crng needs to have been initialized for providing kaslr-seed */
+static int random_ready;
+
+static void random_ready_notified(struct random_ready_callback *unused)
+{
+ random_ready = 1;
+}
+
+static struct random_ready_callback random_ready_cb = {
+ .func = random_ready_notified,
+};
+
+static __init int init_random_ready_cb(void)
+{
+ int ret;
+
+ ret = add_random_ready_callback(&random_ready_cb);
+ if (ret == -EALREADY)
+ random_ready = 1;
+ else if (ret)
+ pr_warn("failed to add a callback for random_ready\n");
+
+ return 0;
+}
+late_initcall(init_random_ready_cb)
+
static int setup_dtb(struct kimage *image,
unsigned long initrd_load_addr, unsigned long initrd_len,
char *cmdline, unsigned long cmdline_len,
@@ -53,6 +81,7 @@ static int setup_dtb(struct kimage *image,
void *buf = NULL;
size_t buf_size, range_size;
int nodeoffset;
+ u64 value;
int ret;
/* check ranges against root's #address-cells and #size-cells */
@@ -85,6 +114,8 @@ static int setup_dtb(struct kimage *image,
/* can be redundant, but trimmed at the end */
buf_size += fdt_prop_len(FDT_PSTR_BOOTARGS, cmdline_len);
+ buf_size += fdt_prop_len(FDT_PSTR_KASLR_SEED, sizeof(u64));
+
buf = vmalloc(buf_size);
if (!buf) {
ret = -ENOMEM;
@@ -164,6 +195,20 @@ static int setup_dtb(struct kimage *image,
}
}
+ /* add kaslr-seed */
+ fdt_delprop(buf, nodeoffset, FDT_PSTR_KASLR_SEED);
+ if (random_ready) {
+ get_random_bytes(&value, sizeof(value));
+ ret = fdt_setprop_u64(buf, nodeoffset, FDT_PSTR_KASLR_SEED,
+ value);
+ if (ret) {
+ ret = -EINVAL;
+ goto out_err;
+ }
+ } else {
+ pr_notice("kaslr-seed won't be fed\n");
+ }
+
/* trim a buffer */
fdt_pack(buf);
*dtb_buf = buf;
--
2.18.0
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