arm64: Add support to supply 'kaslr-seed' to secondary kernel

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@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

0 files changed, 0 insertions, 0 deletions