Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) ===========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) KASLR for Freescale BookE32
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) ===========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) The word KASLR stands for Kernel Address Space Layout Randomization.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) This document tries to explain the implementation of the KASLR for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) Freescale BookE32. KASLR is a security feature that deters exploit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) attempts relying on knowledge of the location of kernel internals.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) Since CONFIG_RELOCATABLE has already supported, what we need to do is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) map or copy kernel to a proper place and relocate. Freescale Book-E
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) entries are not suitable to map the kernel directly in a randomized
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) region, so we chose to copy the kernel to a proper place and restart to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) relocate.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) Entropy is derived from the banner and timer base, which will change every
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) build and boot. This not so much safe so additionally the bootloader may
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) pass entropy via the /chosen/kaslr-seed node in device tree.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) We will use the first 512M of the low memory to randomize the kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) image. The memory will be split in 64M zones. We will use the lower 8
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) bit of the entropy to decide the index of the 64M zone. Then we chose a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) 16K aligned offset inside the 64M zone to put the kernel in::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)     KERNELBASE
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31)         |-->   64M   <--|
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32)         |               |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)         +---------------+    +----------------+---------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)         |               |....|    |kernel|    |               |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35)         +---------------+    +----------------+---------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)         |                         |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)         |----->   offset    <-----|
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39)                               kernstart_virt_addr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) To enable KASLR, set CONFIG_RANDOMIZE_BASE = y. If KASLR is enable and you
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) want to disable it at runtime, add "nokaslr" to the kernel cmdline.