This patch adds the support to supply 'kaslr-seed' to secondary kernel,
when we do a 'kexec warm reboot to another kernel' (although the
behaviour remains the same for the 'kdump' case as well) on arm64
platforms using the 'kexec_load' invocation method.
Lets consider the case where the primary kernel working on the arm64
platform supports kaslr (i.e 'CONFIG_RANDOMIZE_BASE' was set to y and
we have a compliant EFI firmware which supports EFI_RNG_PROTOCOL and
hence can pass a non-zero (valid) seed to the primary kernel).
Now the primary kernel reads the 'kaslr-seed' and wipes it to 0 and
uses the seed value to randomize for e.g. the module base address
offset.
In the case of 'kexec_load' (or even kdump for brevity),
we rely on the user-space kexec-tools to pass an appropriate dtb to the
secondary kernel and since 'kaslr-seed' is wiped to 0 by the primary
kernel, the secondary will essentially work with *nokaslr* as
'kaslr-seed' is set to 0 when it is passed to the secondary kernel.
This can be true even in case the secondary kernel had
'CONFIG_RANDOMIZE_BASE' and 'CONFIG_RANDOMIZE_MODULE_REGION_FULL' set to
y.
This patch addresses this issue by first checking if the device tree
provided by the firmware to the kernel supports the 'kaslr-seed'
property and verifies that it is really wiped to 0. If this condition is
met, it fixes up the 'kaslr-seed' property by using the getrandom()
syscall to get a suitable random number.
I verified this patch on my Qualcomm arm64 board and here are some test
results:
1. Ensure that the primary kernel is boot'ed with 'kaslr-seed'
dts property and it is really wiped to 0:
[root@qualcomm-amberwing]# dtc -I dtb -O dts /sys/firmware/fdt | grep -A 10 -i chosen
chosen {
kaslr-seed = <0x0 0x0>;
...
}
2. Now issue 'kexec_load' to load the secondary kernel (let's assume
that we are using the same kernel as the secondary kernel):
# kexec -l /boot/vmlinuz-`uname -r` --initrd=/boot/initramfs-`uname
-r`.img --reuse-cmdline -d
3. Issue 'kexec -e' to warm boot to the secondary:
# kexec -e
4. Now after the secondary boots, confirm that the load address of the
modules is randomized in every successive boot:
[root@qualcomm-amberwing]# cat /proc/modules
sunrpc 524288 1 - Live 0xffff0307db190000
vfat 262144 1 - Live 0xffff0307db110000
fat 262144 1 vfat, Live 0xffff0307db090000
crc32_ce 262144 0 - Live 0xffff0307d8c70000
...
Signed-off-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
---
kexec/arch/arm64/kexec-arm64.c | 135 +++++++++++++++++++++++++++++------------
1 file changed, 97 insertions(+), 38 deletions(-)
diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
index 62f37585b788..2ab11227447a 100644
--- a/kexec/arch/arm64/kexec-arm64.c
+++ b/kexec/arch/arm64/kexec-arm64.c
@@ -15,6 +15,11 @@
#include <linux/elf-em.h>
#include <elf.h>
+#include <unistd.h>
+#include <syscall.h>
+#include <errno.h>
+#include <linux/random.h>
+
#include "kexec.h"
#include "kexec-arm64.h"
#include "crashdump.h"
@@ -392,11 +397,13 @@ static int fdt_setprop_range(void *fdt, int nodeoffset,
static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
{
uint32_t address_cells, size_cells;
- int range_len;
- int nodeoffset;
+ uint64_t fdt_val64;
+ uint64_t *prop;
char *new_buf = NULL;
+ int len, range_len;
+ int nodeoffset;
int new_size;
- int result;
+ int result, kaslr_seed;
result = fdt_check_header(dtb->buf);
@@ -407,47 +414,99 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
result = set_bootargs(dtb, command_line);
- if (on_crash) {
- /* determine #address-cells and #size-cells */
- result = get_cells_size(dtb->buf, &address_cells, &size_cells);
- if (result) {
- fprintf(stderr,
- "kexec: cannot determine cells-size.\n");
- result = -EINVAL;
- goto on_error;
- }
+ /* determine #address-cells and #size-cells */
+ result = get_cells_size(dtb->buf, &address_cells, &size_cells);
+ if (result) {
+ fprintf(stderr, "kexec: cannot determine cells-size.\n");
+ result = -EINVAL;
+ goto on_error;
+ }
- if (!cells_size_fitted(address_cells, size_cells,
- &elfcorehdr_mem)) {
- fprintf(stderr,
- "kexec: elfcorehdr doesn't fit cells-size.\n");
+ if (!cells_size_fitted(address_cells, size_cells,
+ &elfcorehdr_mem)) {
+ fprintf(stderr, "kexec: elfcorehdr doesn't fit cells-size.\n");
+ result = -EINVAL;
+ goto on_error;
+ }
+
+ if (!cells_size_fitted(address_cells, size_cells,
+ &crash_reserved_mem)) {
+ fprintf(stderr, "kexec: usable memory range doesn't fit cells-size.\n");
+ result = -EINVAL;
+ goto on_error;
+ }
+
+ /* duplicate dt blob */
+ range_len = sizeof(uint32_t) * (address_cells + size_cells);
+ new_size = fdt_totalsize(dtb->buf)
+ + fdt_prop_len(PROP_ELFCOREHDR, range_len)
+ + fdt_prop_len(PROP_USABLE_MEM_RANGE, range_len);
+
+ new_buf = xmalloc(new_size);
+ result = fdt_open_into(dtb->buf, new_buf, new_size);
+ if (result) {
+ dbgprintf("%s: fdt_open_into failed: %s\n", __func__,
+ fdt_strerror(result));
+ result = -ENOSPC;
+ goto on_error;
+ }
+
+ /* fixup 'kaslr-seed' with a random value, if supported */
+ nodeoffset = fdt_path_offset(new_buf, "/chosen");
+ prop = fdt_getprop_w(new_buf, nodeoffset,
+ "kaslr-seed", &len);
+ if (!prop || len != sizeof(uint64_t)) {
+ dbgprintf("%s: no kaslr-seed found: %s\n",
+ __func__, fdt_strerror(result));
+ /* for kexec warm reboot case, we don't need to fixup
+ * other dtb properties
+ */
+ if (!on_crash)
+ goto free_new_buf;
+
+ } else {
+ kaslr_seed = fdt64_to_cpu(*prop);
+
+ /* kaslr_seed must be wiped clean by primary
+ * kernel during boot
+ */
+ if (kaslr_seed != 0) {
+ dbgprintf("%s: kaslr-seed is not wiped to 0.\n",
+ __func__);
result = -EINVAL;
goto on_error;
}
- if (!cells_size_fitted(address_cells, size_cells,
- &crash_reserved_mem)) {
- fprintf(stderr,
- "kexec: usable memory range doesn't fit cells-size.\n");
+ /*
+ * Invoke the getrandom system call with
+ * GRND_NONBLOCK, to make sure we
+ * have a valid random seed to pass to the
+ * secondary kernel.
+ */
+ result = syscall(SYS_getrandom, &fdt_val64,
+ sizeof(fdt_val64),
+ GRND_NONBLOCK);
+
+ if(result == -1) {
+ dbgprintf("%s: Reading random bytes failed.\n",
+ __func__);
result = -EINVAL;
goto on_error;
}
- /* duplicate dt blob */
- range_len = sizeof(uint32_t) * (address_cells + size_cells);
- new_size = fdt_totalsize(dtb->buf)
- + fdt_prop_len(PROP_ELFCOREHDR, range_len)
- + fdt_prop_len(PROP_USABLE_MEM_RANGE, range_len);
-
- new_buf = xmalloc(new_size);
- result = fdt_open_into(dtb->buf, new_buf, new_size);
+ nodeoffset = fdt_path_offset(new_buf, "/chosen");
+ result = fdt_setprop_inplace(new_buf,
+ nodeoffset, "kaslr-seed",
+ &fdt_val64, sizeof(fdt_val64));
if (result) {
- dbgprintf("%s: fdt_open_into failed: %s\n", __func__,
- fdt_strerror(result));
- result = -ENOSPC;
+ dbgprintf("%s: fdt_setprop failed: %s\n",
+ __func__, fdt_strerror(result));
+ result = -EINVAL;
goto on_error;
}
+ }
+ if (on_crash) {
/* add linux,elfcorehdr */
nodeoffset = fdt_path_offset(new_buf, "/chosen");
result = fdt_setprop_range(new_buf, nodeoffset,
@@ -455,7 +514,7 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
address_cells, size_cells);
if (result) {
dbgprintf("%s: fdt_setprop failed: %s\n", __func__,
- fdt_strerror(result));
+ fdt_strerror(result));
result = -EINVAL;
goto on_error;
}
@@ -467,23 +526,23 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
address_cells, size_cells);
if (result) {
dbgprintf("%s: fdt_setprop failed: %s\n", __func__,
- fdt_strerror(result));
+ fdt_strerror(result));
result = -EINVAL;
goto on_error;
}
-
- fdt_pack(new_buf);
- dtb->buf = new_buf;
- dtb->size = fdt_totalsize(new_buf);
}
- dump_reservemap(dtb);
+ fdt_pack(new_buf);
+ dtb->buf = new_buf;
+ dtb->size = fdt_totalsize(new_buf);
+ dump_reservemap(dtb);
return result;
on_error:
fprintf(stderr, "kexec: %s failed.\n", __func__);
+free_new_buf:
if (new_buf)
free(new_buf);
--
2.7.4
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