mirror of
https://github.com/torvalds/linux.git
synced 2024-11-21 19:41:42 +00:00
17e02586ed
and fix all in-tree references. Architecture-specific documentation is being moved into Documentation/arch/ as a way of cleaning up the top-level documentation directory and making the docs hierarchy more closely match the source hierarchy. Signed-off-by: Costa Shulyupin <costa.shul@redhat.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Jonathan Corbet <corbet@lwn.net> Link: https://lore.kernel.org/r/20230826165737.2101199-1-costa.shul@redhat.com
43 lines
1.7 KiB
ReStructuredText
43 lines
1.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===========================
|
|
KASLR for Freescale BookE32
|
|
===========================
|
|
|
|
The word KASLR stands for Kernel Address Space Layout Randomization.
|
|
|
|
This document tries to explain the implementation of the KASLR for
|
|
Freescale BookE32. KASLR is a security feature that deters exploit
|
|
attempts relying on knowledge of the location of kernel internals.
|
|
|
|
Since CONFIG_RELOCATABLE has already supported, what we need to do is
|
|
map or copy kernel to a proper place and relocate. Freescale Book-E
|
|
parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
|
|
entries are not suitable to map the kernel directly in a randomized
|
|
region, so we chose to copy the kernel to a proper place and restart to
|
|
relocate.
|
|
|
|
Entropy is derived from the banner and timer base, which will change every
|
|
build and boot. This not so much safe so additionally the bootloader may
|
|
pass entropy via the /chosen/kaslr-seed node in device tree.
|
|
|
|
We will use the first 512M of the low memory to randomize the kernel
|
|
image. The memory will be split in 64M zones. We will use the lower 8
|
|
bit of the entropy to decide the index of the 64M zone. Then we chose a
|
|
16K aligned offset inside the 64M zone to put the kernel in::
|
|
|
|
KERNELBASE
|
|
|
|
|--> 64M <--|
|
|
| |
|
|
+---------------+ +----------------+---------------+
|
|
| |....| |kernel| | |
|
|
+---------------+ +----------------+---------------+
|
|
| |
|
|
|-----> offset <-----|
|
|
|
|
kernstart_virt_addr
|
|
|
|
To enable KASLR, set CONFIG_RANDOMIZE_BASE = y. If KASLR is enabled and you
|
|
want to disable it at runtime, add "nokaslr" to the kernel cmdline.
|