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 | 46 +++++++++++++++++++++++++-
1 file changed, 45 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index ab296b98d633..a0a730bd9be6 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/string.h>
#include <linux/types.h>
@@ -28,6 +29,7 @@
#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,
@@ -46,11 +48,38 @@ 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, void *dtb)
{
int nodeoffset;
+ u64 value;
int ret;
nodeoffset = fdt_path_offset(dtb, "/chosen");
@@ -106,12 +135,27 @@ static int setup_dtb(struct kimage *image,
return -EINVAL;
}
+ /* add kaslr-seed */
+ ret = fdt_delprop(dtb, nodeoffset, FDT_PSTR_KASLR_SEED);
+ if (ret && (ret != -FDT_ERR_NOTFOUND))
+ return -EINVAL;
+
+ if (random_ready) {
+ get_random_bytes(&value, sizeof(value));
+ ret = fdt_setprop_u64(dtb, nodeoffset, FDT_PSTR_KASLR_SEED,
+ value);
+ if (ret)
+ return (ret == -FDT_ERR_NOSPACE ? -ENOMEM : -EINVAL);
+ } else {
+ pr_notice("kaslr-seed won't be fed\n");
+ }
+
return 0;
}
/*
* More space needed so that we can add initrd, bootargs,
- * userable-memory-range and elfcorehdr.
+ * userable-memory-range, elfcorehdr and kaslr-seed.
*/
#define DTB_EXTRA_SPACE 0x1000
--
2.19.0
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